The reality of it is that he's just not that good a director. Don't get me wrong he has a very creative mind, excellent cinematic tastes and some great instincts for what makes an exciting scene. However he's never been able to direct actors to save his life, he has a distressing habit of building narratives around set-pieces instead of allowing the narrative to flow organically and of course he tends to depend too much on special effects.
Everything that you say here is true. However, IMO, his positives outweigh his negatives.
Directing actors isn't always a necessary skill when you cast great actors that are capable of making their own choices. Alec Guinness, Ewan McGregor, & Liam Neeson all did fantastic work under him.
Furthermore, "building narratives around set-pieces" and depending too much on special effects are both central staples of modern blockbuster film making.
I also think that Lucas has a knack for understanding epic structure that many other filmmakers don't have. And that structure is the most important part of making a great tentpole film. It's what separates a flawed masterpiece like
Revenge of the Sith from a hot mess like
Jupiter Ascending. Even when the dialogue fails to live up to the story's epic ambitions, it doesn't matter when he has the John Williams score do the talking for him.
And although the prequels were a little rough around the edges, I'll gladly take them over anything J.J. Abrams has ever done (with the possible exception of
M:I:III). I also thought the
Star Wars prequels were much more engaging & fun than Colin Treverrow's tepid work on
Jurassic World. Hell, they're more entertaining than anything that Spielberg has done in the last 17 years!
That said, it will never happen. Disney has made it clear that they have no respect for Lucas or for what he created. And if Lucas were genuinely interested in directing another
Star Wars movie, he wouldn't have sold it to Disney in the first place. Plus, isn't Disney a DGA signatory? So wouldn't Lucas have to rejoin the Director's Guild in order to make a movie for them? 'Cuz that ain't gonna happen!