Adding more spells to a full caster others more versatility to go focus on one role such as being a better blaster, healer or face. Or allowing the bard to spread out into better options in other lists.
Whereas the ranger is given an option they would likely never take unless it was a free choice because full casters have better AOE options that don't eat into their crucial spell slots.
For example you've created a Bard with few damage spells. Magical Secrets allows a Bard to not only swap in Primal attack spells but Arcane and Divine ones as well like Fireball or Spirit Guardians. Or swap in utility like Charms.
Whereas Conjure Barrage competes with Upcasted Hunters Mark and Conjure Animals. Conjure Animals being a spell that a Bard can cast more often.
You're still over-selling magical secrets quite a bit. If the bard could swap spells daily like other spell casters that would be a different story, but the requirement to level up in order to swap spells restricts that very significantly. The character isn't likely going to have fireball and spirit guardians and conjure animals.
Competing with an upcast hunter's mark or conjure animals is the same opportunity cost every spell caster has with every spell they cast. Singling out the spell slot for those singe spells doesn't make any sense because every single concentration spell competes with hunter's mark at all levels. All spell casters cast spells based on the situation.
If the argument is that conjure barrage and conjure volley are poor choices for iconic spells forced on the ranger then that's something I can agree with. When someone says "ranger" those don't fall into what I imagine.
It was bringing up bards as somehow significant that was weird.
Clerics can cast almost any divine spell with divine intervention up to 5th level for a lot of versatility compared to a bard that picks up a spell that they can only change by leveling up. That cleric can access any spell on the cleric list with a long rest and has access to 10 more spells prepped that fall into better blaster / better CC categories by domain. And they have access to better armor than bards or rangers. But you felt the need to call out the bard for that one spell gained for some reason.
Druids cast almost any spell a ranger can and more often as you brought up against bard, and they gain access to circle spells, and they can swap those spells better on a long rest, and they add a subclass feature that bards don't get and rangers do. Druids also access any spell on the spell list when bards have access to a few known and those circle spells gained also add to the options like domain spells. Again, you felt the need to call out bards for access to a spell.
Wizards gain a subclass ability and create spell at those levels. They can also swap out to any spell in their book and have greater access to their primary spell list than bards do with those additions to the book. They also have greater access to spells because they don't need to prepare rituals.
Bringing up magical secrets doesn't make much sense. Bards do not have access to the full spell list they chose like clerics, druids, or wizards. They have access to the spells they selected from within those lists. Clerics, druids, and wizards all have access to more spells and can easily change the spell to which they have access. Magical secrets doesn't change that. Magical secrets broadens the availability from which to choose but the bard is still limited to spells actually selected and will never have access to any full list in game play. They certainly don't have that broad range domain spells or circle spells provide. The only benefit is a broad range of a few choices in high level spells, and that's going to be a few spells while those other classes can access all the spells on their list via rest; ie more actual spells available.
Most classes, including rangers, gain a subclass ability in the level range you were bringing up. Bards and clerics do not. Let's compare an 11th level bard to an 11th level ranger.
Our bard is trying to be like the ranger for the purposes of this discussion because "bards make better rangers than rangers" comes up. Valor college for the weapon proficiencies and armor training.
The bard takes the primal spell list. All the sample backgrounds suck for this style of bard so a custom background is required. Wood Elf for both.
(insert background name here -- maybe "hippie treehugger")
Ability Scores: +2 CHA, +1 DEX
Skill Proficiencies: survival, nature
Tool Proficiency: herbalism kit
Language: Sylvan
Feat: tough
Racial abilities: darkvision 60', elven lineage, fey ancestry, keen senses, trance
Skill proficiencies: perception (expertise), survival (expertise), nature (expertise), stealth (expertise), athletics, persuasion
Skill bonuses: athletics (+5); acrobatics (+5), sleight of hand (+5), stealth (+11); arcana (+1), history (+1), investigation (+1), nature (+7), religion (+1); animal handling (+2), insight (+2), medicine (+2), perception (+8), survival (+8); deception (+7), intimidation (+7), performance (+7), persuasion (+9)
AC: 18 (breastplate, shield, DEX bonus)
hp: 102
Ability Scores (default spread)
STR: 13 (+1 save)
DEX: 16 (+7 save)
CON: 14 (+2 save)
INT: 8 (-1 save)
WIS: 10
CHA: 20 (+9 save)
Spells
level 0: druidcraft, shillelagh, guidance, resistance, thunderclap
level 1: longstrider, detect magic, healing word, goodberry, speak with animals
level 2: pass without trace, lesser restoration, suggestion, alter self
level 3: conjure animals, mass healing word, dispel magic, revivify
level 4: polymorph, conjure woodland being
level 5: greater restoration, scrying
level 6: heal
What you seem to be missing is that there are only so many spells for fitting into the theme or role in the first place. Slowly deviating outside of the original spell list doesn't have the room within the spells prepared on the bard to do much just by giving more choices at higher levels. This sample list did swap in a couple of spells on what's essentially a healing (melee) bard but the healing bard still needed the higher level healing spells that are already on the main list because the bard will match the main list to the role or theme initially. Any other spell that might be chosen gives something up from this list. Two lower level primal spells were already swapped in from the arcane list so the build would be giving up greater restoration, scrying, or heal for spells from a different list.
That bard would also have 5 bardic inspiration d10's per short rest. Useful and this looks like an interesting build for me to play but there's nothing I see that's powerful in adding a couple of spells that other classes can cast just as well if not better.
Our ranger can start with something iconic like the guide background. Same wood elf for a direct comparison. I was flip flopping on subclass because they all have clear advantages and went with fey wanderer for the example because it's an example of adding spell lists like we see with clerics, druids, and paladins.
Ability Scores: +2 WIS, +1 DEX
Skill Proficiencies: stealth, survival
Tool Proficiency: cartographer's tools
Language: Giant
Feat: magic initiate (primal)
Racial abilities: darkvision 60', elven lineage, fey ancestry, keen senses, trance
Skill proficiencies: perception (expertise), survival, nature, stealth (expertise), athletics, investigation, persuasion
Skill bonuses: athletics (+5); acrobatics (+3), sleight of hand (+3), stealth (+11); arcana, history, investigation (+4), nature (+9), religion; animal handling (+5), insight (+5), medicine (+5), perception (+13), survival (+9); deception (+4), intimidation (+4), performance (+4), persuasion (+8)
Terrains: coast, forest, grassland, mountains
Weapon Mastery: club, longbow
Fighting Style: dueling
AC: 18 (breastplate, shield, DEX bonus)
hp: 92
thp (tireless): ~47.5
Ability Scores (default spread)
STR: 13 (+5 save)
DEX: 16 (+7 save)
CON: 14 (+2 save)
INT: 10
WIS: 20 (+5 save)
CHA: 8 (-1 save)
Spells
level 0: druidcraft, shillelagh, guidance
level 1: longstrider, detect magic, hunter's mark, charm person, healing word, goodberry, speak with animals, ensnaring strike, thunderwave
level 2: pass without trace, misty step, lesser restoration, enhance ability
level 3: conjure barrage, dispel magic, conjure animals, mass healing word
level 4: conjure woodland being
Both examples wear medium armor, use shields, have extra attack, and can use the same weapons. The bard uses the subclass and 1st level feat to lean into a melee build. The difference is the ranger (who used the subclass and 1st level feat to lean into magic) inflicts substantially more damage with the fighting style and bonus psychic damage from the subclass.
The "bards can add shield for big AC" doesn't work because the bard has to give something up for it and any class can use the background feat to do the same thing. This ranger would have just needed to use a different magic initiate feat to pick up the shield spell. But unlike the bard who would eat through spell slots using it, the ranger could use it and still have those free hunter's mark castings.
The ranger is also has better movement speed while simultaneously slowing targets down with weapon mastery for harrying or kiting.
Both builds are stealthy, but the ranger has better perception because of the difference in primary ability scores. The ranger doesn't lose out as a party face because the subclass grants WIS bonus to CHA checks and the charm person spell, and the ranger can add advantage with enhance ability. I would argue the ranger is the better party face. The bard can become better, but without easy access to swapping spells like the ranger has that requires giving something else up.
That ranger can nuke AoE damage too. Combat, face, stealth, healing, AoE. That was the claim for the bard but I can build that on a ranger.
Both builds have 18 prepared spells. The bard has more cantrips but the ranger can swap out mass healing word for nondetection or call lightning. The bard's only advantage in the versatility part with spells is the earlier access to higher level spells, and those are very limited in slots.
The bard can cast 4 1st level spells, and longstrider once for free. The ranger can cast 4 1st level spells, longstrider once for free, detect magic not as a ritual once for free, and hunter's mark 5 times for free. The bard can cast 3 2nd level spells and pass without trace once for free. The ranger can do the same thing. Both can cast 3 3rd level spells.
Fey wanderer grants conjure woodland being earlier than the spell progression allows, gives a free casting, and adds a casting version that doesn't require concentration. You've brought up conjure animals multiple times but that spell costs concentration so it's doesn't work well with hunter's mark. This is why I pointed out that rangers add a subclass feature bards do not. A subclass addition is a feature of the class progression too, and those can be good abilities.
In higher levels this ranger can use those 3rd level slots for an 8 hour hunter's mark (or use all the free ones) and conjure animals is less useful than conjure woodland being because of the concentration so are are slots available for conjure barrage or some other spell.
Circling back, a spell or two or three from outside the primary spell list doesn't do what you claim as well as lists of spells acquired earlier on other classes.