Windu uses vaapad to create a superconducting loop off of Bane's spirit which is suffering in eternal agony and presumably hatred. He stomps.
If he can't do that, Luke probably wins. I don't think the gap between base-Windu and DE Palpatine could have been closed by Leia unclogging Luke's mind and "unlocking hidden reserves". Luke in RotJ was already a match for Vader as a duelist; it's been quite a while and characters comment on his noticeable improvement, he's almost certainly surpassed Windu.
JA Luke would probably lose though lol.
Sidious defeated Luke more easily in DE, but of course there are circumstances that need to be factored between the two fights.
I'm not too sure. Mace is still the more experienced fighter, Luke the more natural one. He was already on par with Vader (which is very close to Mace) by RotJ, in six more years, I'd imagine that he'd surpass Mace in skill given his astonishing rate of learning, but I don't recall any feats to suggest that would be the case.
Sidious was on a dark side nexus the first time, and Luke is more powerful/mentally clearer in the second. Also I think it's tough to deduce how comparatively poorly they were doing against Sidious from comic panels.
I don't think RotJ Vader is on Mace's level with a blade, but given Luke's growth curve, he's probably surpassed him as you stated.