What are your thoughts on how the epic boons stack up?
I'm going to go through your list, but modified for a table where only 1/3 of the challenges are combat, and the other challenges are just as, well, challenging as a 19th+ level combat. You're more generally applicable, this is just an alternate viewpoint.
Combat Prowess: once per round, turn one miss into a hit. "A" tier for martial classes, "S" tier for rogues. If you have a lot of attacks, you are likely to use this once per turn, and if you rely heavily on a single attack and need to make sure it hits (i.e. you're a rogue), this seems essential.
Combat only, "C".
Dimensional Travel: after taking the magic or attack action, you may immediately teleport up to 30 feet to an unoccupied space you can see. "A" tier for any class. This is just incredibly valuable in so many situations. And fun!
Useful in and out of combat, as long as you have ways to trigger a Magic Action without using resources. "B".
Energy Resistance: you gain resistance to TWO damage types, excluding bludgeoning, piercing, slashing, or force, and can change those resistances after a long rest. Also, if you take damage from one of those types that you are resistant to, as a reaction you may do 2d12+con modifier damage of the same type to any creature you can see that is within 60 feet and doesn't have total cover, unless they make a dex save (DC 8+con modifier+proficiency bonus). Whew. "C" tier for any class...maybe "B" if you are a specific type of tank. Maybe. The damage redirect is fairly worthless at high levels, so really it just gives you two resistances that you can change. Which is...okay, but resistance isn't too hard to come by at level 19 if you really need it.
While there exist some clever uses for non-combat challenges, this is mostly combat only, and even there only some combats. "D".
Fate: whenever any creature succeeds OR fails on a d20 test, you can add OR subtract 2d4 from the roll; resets every time you roll initiative or after any rest. "S" tier. Amazing. As a DM, I kind of hate it because failures make the story more fun, but having this once per combat is going to be clutch so often.
This is great, almost every challenge will have a d20 test being made for or against the party. You can use it for a social challenge and it recharges for a combat, but not vice-versa. Still, so applicable. "S".
Fortitude: add 40 to you hit points, and, once per turn, whenever you regain hit points for any reason, add your constitution bonus to the healing. "C" tier. Basically the toughness feat with a little kicker added on. As epic boons go, doesn't feel that epic.
HPs can be important in a variety of challenges, and increasing in- and out-of combat healing should be generally useful. For those with lower HD sizes this is better, say up to +25% HPs. Still, "C" for those with a good CON mod, lower otherwise.
Irresistible Offence: your bludgeoning, piercing, and slashing attacks ignore resistance, and when you roll a 20 to hit with an attack (not when you score a critical), add damage equal to the ability SCORE raised by this boon. Maybe "C" tier? With the current rules, it's "D-C" tier. That damage bonus seems huge, but it's really not - basically, it adds 1 damage on average to each attack, so the more attacks (or rolls with advantage) the better. But IF magical weapons no longer allow you to ignore resistance to bludgeoning, piercing, and slashing attacks and that resistance remains relatively common, then this might get up to a "B" tier for...well, for fighters and barbarians, basically. It would sure be fun when you do roll a 20, though!
Combat only, and not nearly as nice as Combat Prowess, so "D".
Night Spirit: when in dim light or darkness, can give yourself the invisible condition as a bonus action, ending when you take any action, bonus action, or reaction, and you have resistance to anything but radiant or psychic damage. "C-A" tier, depending on character build. Okay on any character, but it is not hard to see how you could create some pretty strong builds around this boon.
This can help with a variety of challenges, but since it's self-only, at 19th if a challenge can be overcome by a single person being sneaky you probably already have that covered. The resistance can be more generally useful. As written if you're not using your bonus action in combat you can just activate this every round. "C", maybe "B".
Recovery: Two parts: (1) Last Stand: When you would be dropped to 0 hit points, you go to 1 HP instead, AND gain HP equal to half your maximum. Once per long rest. (2) Vitality: you have a pool of 10d10 and as a bonus action may roll as many of those dice as you like, healing for the total. Replenishes on a long rest. "A" tier, "S" tier for frontline combatants, unless they are already barbarians. Soooooo much better than fortitude.
As Fortitude, HPs are occasionally useful outside of combat, but not always. This provides 10d10 personal healing which will be a lot more healing that +CON per heal of Fortitude. This helps more against a single issue per day, Fortitude can help multiple times per day. Still, given the nature of challenges that eat HPs plus the better healing boost but the scaling 1/day HP recovery that doesn't leave behind those classes with more HP, this is better than Fortitude, so "B".
Skill: gain proficiency in all skills, and expertise in one. I dunno..."C" tier? At best? By this level, your party mostly has skill checks covered. Fun at an individual level, I guess. If you're not already a bard or something. Would be pretty interesting on rogues with reliable talent.
By 19th level, I think you'll probably have ways to deal with all of the common challenge skills your DM uses. Maybe this is useful for a one-shot, or for a 1-2 person party, but otherwise it's redundant. "D".
Speed: increase movement by 30 feet, can disengage as a bonus action, which also ends grapple on you. "A" tier. Grapple is going to be used so much more now, so that alone makes it a pretty awesome boon, and an extra 30' of movement is great on anyone (monks would have a base move of 90!).
Extra movement can help with some challenges, and a lot in combat. Cheap disengage can be good if you don't have other uses for your bonus actions. Still, mostly combat, "C" for those that can take advantage of it, "D" otherwise.
Spellcasting: when you cast a level 1-4 spell, roll a D4 and if your roll matches the spell level, it isn't lost. "D" tier. At this level you might succeed on this 1-2 times per combat. So it's basically like having a ring of spell storing, except it's random. Fun for gamblers, I suppose.
Spell Recall isn't quite what is written here, it spell slot used not spell level. Basically it's a 25% chance to not expend a slot level 1-4. For casters with a lot of reaction spells like Shield, Absorb Elements, Silvery Barbs, Counterspell that make good and frequent use of lower level slots, this could be a big boost if they regularly run out of spells. It also can be useful for a half-caster where this will cover almost every spell they cast. Note that it is cast, not expend. So this doesn't count for things like Divine Smite.
That said, if you don't run out of spell slots, then it's worth is minimal. Maybe more psychological, allowing you to use utility spells outside of combat without as much worry.
So this is highly GM dependant. If you regularly run out of spell, having more is a godsend, "A". But show me the 19th level character thar regularly casts that many spells, I think that's super rare. If you occasionally run out of spells, this is a minor boost, "C". If you don't run out of spells, and this is likely where most 19th level characters are, then it's not worth it at all, "F".
Not a reasonable use, but an amusing one would be with a Diviner, who regains a slot 1 level lower than used when casting Divination spells. Then they have fun with divination spells levels 1-4, including (upcast) Mind Spike.
Truesight: you have truesight to 60'. "B" tier, depending on character build. Always handy, occasionally clutch.
Right on the money. "B".