Well, Waid has made public statements to the effect of regretting what he did with Diana in KC; if he feels he could have done better by her, that implies a degree of influence and therefore culpability in the way she turned out. And he had a few rocky moments with her in JLA as well (Fairy Tales, again), that seemed to echo some of the problems from KC (namely, something that looked like her story and affected her more than anyone but in the end was actually about someone else). I will readily agree that Ross probably carries the lion's share of the blame, though; if it were up to me, he'd never touch her, while I'd cheerfully, at this point, give Waid a one-shot or mini or Elseworlds or a Superman/Wonder Woman weekly or what-have-you to play with her as he wished.