I don't really follow what your collective expectations for the writers are and what you believe that they are and aren't allowed to write about.

The circumstances around why the civilization of the Plenty ended are open to interpretation. Was it the ennui of the lives that they created for themselves? Was it the fact that eliminating interpersonal conflict comes at the cost of individuality and diversity? That the first external entity (Meteion) that their civilization encountered raised an existential crisis that their singular hivemind couldn't handle? Either way, the exact mechanism is left to you, the player, to interpret.

'Though worlds apart, these peoples shared a belief. The belief that they had tried their best. That they had tried to achieve their potential, with every step and success. In the course of which they learned the truth. That they would never be free of anger and sorrow, of fear and despair - as long as they yet lived.'

The only point that's really being made through these examples is that all things come to an end, no matter how 'well designed' they are. Which is not a controversial point at all. It just seems strange to me to try to argue that the Amaurotines are somehow the exception to this rule, where all these other more advanced civilizations have failed. It's not an indictment. And if our emotions - things like anger, fear, sorrow, and despair - are a part of us, then perhaps the solution is not to redesign the environment such that we never have to experience them. Perhaps the solution is to change ourselves, and learn to live with and adapt to them. It's almost like some defense mechanisms are just better choices than others. Again, not a radically controversial idea.

I don't think any of these objections that we're seeing are actually 'thematic', though. There'd be an equally loud outcry to anything suggesting that the Amaurotine society wasn't as 'perfect' as they pretended that it was.