Percy has changed a great deal. A lot of it is unhealthy
Wow. Really impressed by this detailed analysis of Percy's character, by all the thinking you've clearly put into it. No wonder he comes across with all kinds of interesting psychological undertones.
*nods at every point in list*

Warning: Entirely theoretical rambling follows -- discard at will:
I'm imagining him using that bottomless well of endurance with Snape. A kind of remote and untouchable patience.
Now this is my imagination, but in addition to the other changes in his character, I was also impressed by his ... untouchability(?). I mean, he struck me as having learned endurance in a kind of bone-deep (Bhuddist?) sort of a way -- and Snape may be controlled, but he's stormy inside, while this new Percy seems just quiet and still (because, yeah, hopeless).
So I imagined that Snape might rage at him and he wouldn't react -- I think I saw his hopelessness as a kind of inner strength, something that gave him an edge over Snape, actually. Er.
In any case -- thanks for the utterly fascinating fic and characters and ideas!