I think I'm comfortable at this point with saying that I'm in the top 99+% of writers - I've been picking up "real" books and trying to read them and finding that they seem visibly badly-written to me now that I've written HPMOR. Though I'm still not in the literal top tier; there are basic things in writing that I still don't do too well, despite being outstanding in others, and my new level of skill is just enough to start noticing that Neil Gaiman and Terry Pratchett are doing things way the hell above me.

What of Pratchett's work are you judging by? Middle-Pratchett is top tier, but I'm much less impressed with recent-Pratchett (going back at least a few years before the Alzheimer's diagnosis.)

I get the feeling that a lot of the top experts at writing aren't necessarily experts on writing, because they can and do lose their touch without noticing that something is wrong.