It's not that I want them to totally change as characters but I do expect them to be something more than they were to start(which, to be fair, some are but not to a degree where it really felt like they were changed by what happened). Some of the slinks do help the characters develop more but it's never addressed anywhere else which is super lame! And I disagree with them being fully developed. You're mistaking distinct personalities for character depth. Their personalities give them their terrific attitudes/roles but I don't think there's any inherent depth because of them. Depth comes from their personal growth through the story which I would have liked to see more of. I don't want to keep going back to Dojima but his arc really is the most well realized one in the game. His slink directly relates to plot points and it's super meaningful.The argument that the P4 characters aren't developed doesn't sit right with me at all. They're fully fleshed out and defined by distinctive personality traits. Basically, they're fully developed characters that don't go through significantly more development throughout the game. They've lived their entire lives as ordinary teenagers, so a significant change in temperament would be jarring. In fact, I'd posit that their "wild ass adventure" would prevent them from growing as people, since its a problem they're singular focused on. (though confronting their shadow was a huge deal). Really, i'm not sure how you'd have them change as characters. Because they "do" change, but in a natural, subtle way (unlike in P3, due to the reasons listed by Flux)
Your second point is entirely subjective. I personally think that each of the main casts social links enhance them to a suitable degree (and in Kanji's case, its nearly fucking mandatory for his character)
Also think it's ridiculous to say that this life altering situation they're put into would prevent them from growing as people. Should be exactly the opposite, it should be a catalyst for meaningful change in their lives.