the biggest thing I see in this thread that would help fix(but not fully fix) the Mentor System is to remove the EX and savage content from the Mentor Roulette. That stuff should not be there at all and is the very reason I never bothered to unlock mentor roulettes in the first place. I'm not even going to bother unlocking mentor again as long as they leave it like that.
the second thing mentioned in this thread is updating the Hall of the Novice to teach players the newer more difficult content. I can see this being a forced thing if you want to unlock EX and Savage content(as well as newer content with higher difficulties. I would love to have something like this I can repeat till I feel comfortable enough doing this content.
I honestly have no faith the devs will even try to fix the mentor system in any way which is a shame.