I think that many are missing out on the more fairy tale style stores of 90s Trek and even the TOS style films ("second star to the right; and straight on 'til morning"). But, you are quite right that the Federation was never going to be forever but seeing it happen is probably less appealing.I get that, but I'm also realistic about how great civilizations rise and fall. Nothing is truly infallible. That doesn't mean what came before no longer matters just because in hundreds of years it went downhill. That's a very nihilistic viewpoint to take. It always matters, especially when it comes to picking one's self up.
It's one thing to have it hinted at and another to see it done.Even Berman Era Trek hinted the future Federation could collapse because of external influences or attacks or not even exist at all because of the same. This kind of ties in with some future glimpses we've seen of humanity and the Federation from alternate timelines that were avoided or repaired.