Mythic and Pugs are pretty contradictory words. At least they should be still at this point. I'd have to say that I strongly disagree that a boss that's 6 bosses into the raid is badly designed because a pug can't kill it. Heck I feel that way about Heroic as well.
Anyway, while I've stepped back to just Heroic raiding this expansion, I believe that the difficulty curve has been pretty good and the bosses interesting enough. The environment itself doesn't "wow" me, but it is maybe the best entry raid we've had as far as I can remember.