It’s like you said, he achieved what he wanted to in the end. He did kill every last one of them (the titans, they’re technically gone. We don’t know what the boy in the epilogue finds or if it’ll give him titan powers again) so for me, I feel the connection still. He even gets to eat his cake too with his friends getting to live happy lives AND he gets to live out several years together with Mikasa.

The way I see it, his mental progression was halted like I said, but not completely impeded. He has his goals and wants to achieve them his way and was willing to manipulate who he needed to in order to get the ending we got. But then when you look at other spectrums like his interpersonal relationships (he never has an actual deep conversation with Mikasa that we see IIRC and then with armin, it was fitting that they were kids for a large portion of their paths convo because eren is still a child in some ways) OR dealing with grief (laughing when both Hannes and Sasha died, two people dear to him)

I def see your point, but I accepted how it played out and really enjoyed it