I like this idea of stagnation being the issue and not so much identifiability. We don't always identify with our characters, and that's why some roleplayers like to write nefarious villain characters that are totally devoid of any commonplace human morality.
For me, however, I'm not even sure that predictability is necessarily the issue so much as the metagame involved in such a character — I'll specify that here I mean metagame in the literal sense of the game outside of the game, which is to say the emotions and behaviors of the writers towards each other through their characters. I can appreciate an honest-to-goodness in-canon OP character "if done right". But the more I've thought on this matter, the more I've noticed that it's not as if the roleplayer is necessarily doing something teachable and definite that I can really say gives their character more dynamics.
There's a huge difference between a character who has been written for the author's self-glorification and a character that exists as an element of a story. When a roleplayer becomes fixated on the concept of winning, it's glaringly obvious (and we sometimes call it main character syndrome, it's so common) that they have no significant interest in the story or anybody else's characters or ideas or opinions. They just want to beat up the rebellious peons, save the princess, and call it a day. Everybody else can just be fallible or whatever it is those other people do.
Then you've got a character who's just bonafide OP, like Superman, or genuinely perfect, like a lot of strong secondary characters are in more idealistic media. These are not unilaterally boring characters because they are written for other reasons. I think my biggest point is that character development is not always about overcoming fallacies. It's an underdog arc and that's only one out of a million different ways to write a character and I think the fact that it's been proliferated as the only way to avoid a Mary Sue has significantly diminished a lot of potentially valuable character concepts. Remember those squares they taught you in elementary literature? Man versus Self, Man versus Society, Man versus Man, and so on? We've basically labelled anybody writing a character who isn't part of a Man versus Self arc to be an uncreative roleplayer by saying perfect characters are not interesting.
Okay, let me reel back — woah, Sammy, that's some paradoxically rebellious/not-really-news stuff you're proposing there. Man versus Self is a very natural story because it's one we identify with the strongest; we all experience the empathy gap, and so it's harder for us to process stories that go beyond ourselves. Thus our creativity flows through the path of least resistance and we end up with a lot of tropes that stick to this idea of internal flaws.
I don't know; my mental articulation just dropped about there, but I think I got enough of the point out to get the idea across. o.O