Imo, George was always more of an ideas guy rather than a writer, or even details guy, if that makes sense. Obviously he had some amazing ideas (we wouldn't be talking about this thing called Star Wars if he didn't lol) but when it came to making a coherent story or even passable dialogue he needed help, to put it mildly. I mean, who could forget "around the survivors a perimeter create!" 
If you watch the making of videos for ANH, they actually talk about that. You can write the dialogue, but you can't say it. Basically, it looks good on paper, but no one actually talks that way.
There are cases where writing differently from how people talk works well. Lord of the Rings has a pretty stylized dialogue, but given the setting you just sorta accept it. Honestly, Warhammer also falls under this, given the stilted and archaic way Space Marines often speak (as if they're always giving a speech). I don't think I'd like a purely naturalistic dialogue in Star Wars, rather something based on the slightly-stylized 70s/80s dialogue they had in the original trilogy. It feels natural enough, while still having some of the heightened swashbuckling banter and drama.
I'm more concerned about Lucas' abilities to convey his character motivations through the dialogue. Some of his characters' actions just seem bizarre, or they emote weirdly, or express themselves in a way that isn't really stylized, just weird. Anakin is obviously the epitome of this, but you can find it all through the prequels.
Anyway, we probably don't disagree a whole lot.
