You're all over the place right now.
What does my opinion on final fight has with us arguing whether Corypheus being a schemer? FYI, I think the fight could be longer, maybe a bit more spectacular, but no - I don't have as strong feelings about the final battle as some other people have. It makes sense that Corypheus ended the way he ended, all things considered.
Secondly, would you suggest that a Magister that can wield the power granted through the blood magic of several thousand slaves (even as 1/7 of the conclave), is what you encountered at the endgame?
No, I would not suggest that at all. Corypheus is NOT an ancient magister he was - Old Gods don't guide him anymore, and he himself was corrupted by Blight and slept for a millenium.
He has many sinister powers, but none of them grants him a true god-like might - and what might he has, aside from blight magic, seems to crudely emulate gods of old and comes from the elven orb. Add to that the fact that manipulating it takes quite a bit of his own magic, which eventually faltered, allowing Inquisitor to rip the artifact from his grasp.
His main schtick is that he can't die - NOT that he has infinite powers of some sort. Hence he works and strikes predominantly from shadows or through his lackeys. It's not that he's made out of glass, but it's pretty apparent that he has no power to match his ambitions.
After all, entering the Golden City is one thing - becoming god is another. Even getting out unscathed or not uncorrupted seems to be a tricky thing - and one that Corypheus didn't pull off last time he'd done it.
This thread is about the quality of the last encounter, which many feel is sub-standard. And that is not just my opinion, nor my interpretation of events.
True - whether last battle is up to one's standards is a matter of personal opinion. But it's still not an opinion that is held as widely as you think it is, nor it justifies claims that are simply ridiculous or flies in the face of what story is about.