I'm not gonna throw any shade at the OP, nor do I see any insult in his words, which are eloquently written. And to the person who called four paragraphs and probably 800 words "another 50k word essay", welcome to a forum discussion lol, TikTok is thataway.
I've experienced this death of immersion in other games, including my very first MMO (not City of Heroes). I just can't see in that game what I used to, and it sucks, and I know it would just injure me more for one of its present fans to mistake that fact for some kind of shit talk, so I sympathize with the OP.
The magic of City of Heroes, for me, now that I think about it, is actually that I always had to meet it halfway. Considering how neck-deep I've been in this game in the past, some of my old friends would be surprised to hear this, but there was never a point when the game delivered complete immersion without any effort on my part, especially considering the original dev team's abundance of campiness (no shade here either, just pointing out the obvious).
City of Heroes still works for me because my imagination really likes the work, the magic is still there because I'm still able (and willing) to meet this alternate reality three quarters of the way; and I'm still invested in my roster of characters, enough that I'm probably still more fond of them than any other roster of comic book characters out there (I know some of you can relate!). I grew up playing pen-and-paper games, text adventures, sandboxes and CRPGs with truly shitty graphics, so it's just another Tuesday for me.
But this isn't gloating, it's gratitude. One day I might feel exactly like the OP and not be able to help it. I'm not better than them, just luckier.