I think the only thing to do is give it time. Yes, nothing that's out so far is as good as the best of the old stuff, but the new EU has only been going for a year, and the quality of the now-Legends stuff had been declining for a while anyway. I think it would be a good idea to be less shy about explicitly re-canonizing things from Legends, and if the implication at the end of Aftermath does in fact pan out, I think that'll be a step in the right direction. But really, I think the biggest thing is that we don't have a large enough sample size yet to really know what we're dealing with.

Don't know much about Darth Bane because I never found the Sith to be terribly interesting, but that and KOTOR are so far removed from the films in the timeline that I'd imagine they're not that tied into classic-era continuity anyway. I've always figured the Old Republic stuff probably functions in-universe as "legend", in that it's so distant that its historicity is ambiguous. I always thought that line they had when they rolled out the Legends label about how these are stories that may or may not be true made the most sense when thinking about that distant past stuff. As for Plagueis, I didn't read that one either, but I think a case could be made for re-canonizing it. I seem to remember Lucas somehow granting it higher status than the other books when it came out, and Luceno makes frequent reference to it in Tarkin. I'm not sure if they'd just take the Legends label off the existing book as-is, but it wouldn't surprise me if they brought a lot of that stuff back in.