For the sake of brevity, let's zero in on your first attempt, the Moon Druid. You've claimed that the capstones are worse than the level 17-18 powers. I gave druids as a counterexample. You're trying to refute that counterexample by observing that the capstone isn't that great against "the creatures you'll be facing" and isn't broken. I agree with that observation--it's not broken--but here's the thing: the capstone (unlimited wild shaping) is undeniably better than the level 18 feature (beast spells), which was the claim the counterexample is intended to refute. At level 20, you can freely turn into a bird to go spying, land and switch to a wolf if an eagle tries to eat you (or just become an air elemental and scare it away), turn into an earth elemental to burrow underground, kill a hundred orcs without a sweat due to Onion Druid-ing, and then join a 1st level party in the pose of the ranger's pet mongoose. It completely removes the resource constraint on (admit it!) one of the funnest abilities in the game. At 18th level, the druid won't even attempt to spy in bird form because he's saving wildshaping for air elemental form for emergencies instead... and he can't afford to burn two uses on Earth Elemental to burrow underneath a structure either. In what way is Beast Spells half as transformative as unlimited wildshaping via Archdruid?
Okay, setting aside that overpowered was a goalpost move (its admittedly a knee jerk response at this point), the only reason people think that the Archdruid is really good is due effective infinite THP generation. However, for a level 20 character, playing as a CR 5 critter when facing against CR 20+ threats, it is annoying. Your attacks are weak, your saves are weak, and you're physically ineffective beyond being an ignorable HP buffer.
If not for the fact you have access to spells in wildshape form now, you would have zero threat at this point in the game.
Oh, and do you know who else can do all the above stuff you listed? Any epic level spellcaster through use of polymorphs. All the above, while a good joke, is just messing around and having fun. Flavorful stuff is fun, but hardly powerful; cantrips like Prestidigitation are fun, but no one will say they're powerful. And, yes, we're still talking power.
And it still doesn't touch on the fact that the capstone is only good for Moon Druids. No one even thinks twice about it with a Land Circle, or likely any future non-shifting subclass.
Edit: or were you thinking more of 9th level spell access at 17th level? True Polymorph/Foresight/etc.? That stuff is nice, about as nice as Archdruid in a completely different way... but it's not bigger than Archdruid, nor better. It's just different.
Yes, the 9th level spells are the druid epic benefit. And, yes, they're more
powerful. Fun is not a measurement. If you want to mess around and feign being someone lower level's pet, then you don't need a level 20 ability to do it. If you want to kill a 100 orcs because, then you don't need to be a level 20 character. To scare a hawk? A level 1 character can do it.