The Lucas of the late 70’s - early 80’s is gone. You need to accept that. His ability to craft a story comparable to the OT or TFA has dissipated.
I don’t think so at all, the prequel story was fundamentally good. While his directing ability is questionable, there’s no reason to think that he wouldn’t be able to write a good continuation. Indeed he very likely had a lot of it written out in notes and so on beforehand, talking about the sequel trilogy going as far back as the set of IV. He admits his dialogue isn’t great himself, but that’s not an insurmountable obstacle. Have another writer do a dialogue pass.
Lucas was a pretty good idea man but his ability to execute such things post ROTJ was nil. If anything JJ and Kasdan could have taken a couple of ideas George had and adapted it to Episode VII.