i've read all the extant lucas sources but can hardly quote them chapter and verse, so if that means I have to abstain from the discussion, so be it. i will say that the proof is in the pudding--epIV and epV are better than the prequels to me, and there are probably many reasons, but to me one of them has to be the presence of gary kurtz. he works on the movie, it's good. he doesn't, it's not so good. i may not be able to give you three cited examples of what he did or didn't do to make the early movies better, but they are.
there IS, however, at least one telling piece of evidence extant on mccallum NOT exercising any quality control, or at least, it's telling to me. it's when they're editing episode I in "the beginning," the doc on the epI dvd set, and it's clear this is the moment when they should realize they've got a problem on their hands, and only ben burtt actually speaks up and says something. i can't recall exactly what he says, but it's so revealing because it's the only moment I can recall in the modern star wars coverage where someone within lucasfilm admits to anything but the prequels being godly things of beauty rendered from on high by Godhead George.
as to your assertion that the money/production stuff is what a producer is supposed to do, maybe, but there's also been plenty of examples of creative producers who have been involved to a small or great degree in the creative decisions on a film in collaboration with the director, writer, etc. hell, lucas himself is a towering example of this; his hand is all over Empire and Jedi, whether he directed them or not, in more than just a co-writer way.