Chaosmancer
Legend
Every single monster from the monster manual can force a con save on a spellcaster. From commoners, to Ancient Dragons, to Archmages. As long as a spellcaster has cast one of their most powerful ongoing spells (concentration) and has taken damage, they must save for it.
Wisdom saves are much rarer on monsters. Even with monsters that have it, it usually just hits them with the Frightened condition.
I do take other saves into consideration, too. Had I been defending the bard, I would definitely bring up their dexterity saves, because it allows them to dodge significant damage more reliably. But its not about the bard, its about the sorcerer.
Again, I never see "has X type of save" brought up except as a defense for the sorcerer. If people ask "what is so great about bards" the phrase "They have Dex saves to avoid damage" never comes up.
If you don't know how long you'll need to be invisible, that just emphasizes using extended more. Better to be safe than sorry and take the 2 hours of invisibility than the one. Hiding is still useful. Not all monsters have great Passive Perception. At a +2 dex against PP of 11, you're still likely to succeed. Doesn't hurt to give it the ol' college try, especially since you'll still be invisible after you try.
Sorcerery points are a limited and precious resource, using them in a "might as well, might need it" manner is just wasteful.
And on hiding, you seem to have missed the point. You cast the spell and hide during combat. Now what? You aren't contributing to the combat anymore, because the moment you do your invisibility drops. Are you simply hiding until your party loses the fight? If you just needed to get out of the fight, you are better off simply running away.
Also, if you want to consider a passive perception of 11, being invisible would grant you advantage on stealth checks, giving you a passive 15 stealth, and that is even assuming that during combat you would use a passive perception at all.
So, still, all of this seems very niche and very much just using the ability because you can, not because it is actively helpful in more than a handful of situations.
If your spellcaster needs even a minute more than 1 hour of invisibility (or any effect) its always more efficient to extend it. If there needs to be 4 hours of invisibility, it would cost a wizard 4 2nd-level spell slots. It would cost a sorcerer 2 2nd-level slots and 2 sorcery points. They'll always be more efficient.
The abilities a sorcerer imparts onto their characters aren't necessary flashy, though most non-spellcasting abilities are. Something's usefulness isn't really based on whether you feel it would be helpful at the time, because you usually aren't thinking about what you don't have.
A cleric's channel divinity isn't often praised as a game-changer, yet when a cleric uses them, they actually can change the game meaningfully. The same could be said for a Druid's Wildshape or a Paladin's aura. I'm not ever thinking how useful extra HP could have been or a Paladin's aura may be perfect for our situation when they aren't there. But they are still extremely useful features.
You are missing the point entirely.
Paladin auras, Wildshape and Channel Divinty are active, new effects in the game. As a druid player, I can definetly say that there have been times when using my wildshape has changed the course of the game, because I knew "hey, I can solve this problem with wildshape."
Metamagic doesn't do that.
Continuing with invisibility, let use some set framing.
{X} is all the times invisibility is useful.
{Y} is all the times invisibility is not useful no matter how long it lasts
{X'1} is all the times invisibility would be useful, if invisibility lasted an additional hour.
By logical neccessity, {X'1} must be the smallest of those three sets, because it is between the times that the spell is useful and the times when it is never useful. We can argue all day about the exact size of this set, but it is smaller than the other two.
So a wizard taking Invisibility gets {X} the larger share of all the times casting invisibility is useful to the party. A sorcerer also gets {X}, making them equal, but then adds {X'1} if they take extended spell. Extended spell has not reduced {Y}. It has not given us a situation where Invisibility would not have helped, and made invisibility help.
And think for a moment about the examples you gave me. Wildshape, Paladin Aura's, Channel Divinity. Are those the only things those classes can do?
No
Druids also have ritual casting, a unique spell list, and weapon and armor proficiencies and ways to leverage those proficiencies with decent Hp and spell augments.
Clerics get ritual casting, a unique spell list, weapon and armor proficiencies, Divine Intervention, decent hp and every subclass gets a level 8 damage boost
Paladins get superb hp, all armor, all weapons, non-spell healing, divine sense, divine smite, channel divinities, fighting styles, a unique spell list, extra attack and divine health.
And I'm not talking about specific subclasses, I'm talking about the base class. Each of those abilities you listed that give entirely new actions, buffs or things you can accomplish are part of a set of abilities.
Sorcerers don't get armor. Don't get most weapons. Don't get good health. Don't get a unique spell list. They have con saves and metamagic. And all metamagic does is allow niche uses of spells that other people can cast anyways.