If people want to do something blind that's fine. But it's not blind if they immediately ask what to do. In mentor roulette I will typically wait a few wipes to give input just in case someone is actually wanting to do it blind and because most my advice will likely go over people's heads without context. I think if players do truly want a blind experience it's best to do it through PF as they can specify that's what they want in the description and get the full experience of everyone getting to figure out the content together. DF you might be getting players that will immediately spoil the fight.

As for the expectation that the mentor is the tutorial, there's a limit to what you can explain through text. I remember when I got Tsukuyomi EX in mentor roulette one time, people couldn't understand meteors no matter how hard I tried to explain it. So I ended up having to pull out Photoshop and make a quick diagram, upload it to imgur, and link it. Only then could people understand how that mechanic was done because people weren't understanding it with text and markers. Not every mentor is going to be equipped with an art program and mentors on console wouldn't have been able to do what I did. I think the bulk of ARR EX trials can be easily explained through text, but later fights can get trickier, so looking at a guide before queuing isn't a bad idea.