A world that eventually went to war with itself despite everything being so much better compared to what exists today.

Hydaelyn may have been the one to sunder the world, but she's just the embodiment of an ideal.
Which happened as a result of the world ending. Meanwhile mortal conflicts arise for way more petty reasons and often cause the "world's ending". It's outright stated that the conflict between the Anyder and Convocation was unprecedented among the Amaurotine, the same is far from true on the Source.

That's what we've been told about. We've been shown a glimpse of Amaurot but not the wider world. We don't know if the whole world is "perfect and peaceful" or if it's simply Amaurotine society that works that way.

Also there's nothing to say they had "more fulfilled" lives just because they lived longer. That's all relative anyway. And a whole life in a repressive conformist society might not be all that fulfilling to some people anyway.
I really hope we get to see the ancient world through another civilization's eyes at some point. Get to look at Amaurot through others' eyes. Cause the impression I got from it was that for all the security and wonder it had, it was repressive, particularly of the individual.
I'm sure the world wasn't completely perfect or anything, but so far as we know Amaurot never had any conflicts either within their society or without, and they're noted to be pretty hesitant to assert themselves over other civilizations. As far as conformism goes we really only see that they try to keep to a dress code in order not to engender various social issues. You might say this is repressive, but just compare it to other civilizations on the Source, it has nothing on the likes of Ishgard or Doma/Hingashi or Gridania or Ul'dah. The thing to note here is that the Amaurotine had freedom of thought and speech, and the ability to create whatever they wished and share it with the rest of their society - Again, it's not like there were zero issues here or that it was totally unrestricted freedom, but in a comparison Amaurot practically blows modern societies out of the water.

Furthermore, there isn't any evidence that sundering the world cause "destruction" of their world.
I'm not really sure how to conceive it any other way.