To be fair, in my experience when I get an Extreme in Mentor Roulette, no one has prepared because generally the folks who queued in don't even know what an Extreme is, much less that they might want to read up on mechanics first.
I got Garuda EX a week or two ago in Mentor Roulette, with seven enthusiastic first-time sprouts who had no clue what they'd gotten into. This was the exchange:
Me: Hi! Before we start, do folks know the mechanics to this fight? Because unlike a lot of what you've done so far, you can't easily just brute-force this blindly.
Tank #1: *has already YOLO'd straight across the arena and pulled before I finish typing*
Party: *wipes to adds, unsurprisingly*
Tank #1: Apparently, we do NOT know the mechanics.
Party: *general chorus of agreement with tank #1*
(They hunkered down and we talked about the fight, and got them the clear.)
But once they do understand that, oh, hey, this fight has actual mechanics, it's often tricky to ask them to go look up the fight and read all the instructions, or watch a video guide.
For one, someone may be on a Playstation and not have a laptop handy to go hit up a guide. (And reading some of those guides on a smartphone isn't always easy.) Going "hey, go watch this 8-minute video and remember all of it" isn't necessarily any better. But for another, people in this thread have mentioned before that they learn better from seeing the mechanics; that's true for lots of people.
I tend to figure that once Mentor Roulette drops me into an EX, if the folks there are willing to learn the mechanics, I'm happy to teach them.
If folks are willing to learn the mechanics but want to try the fight blind, I'm also open to that; there was a fairly fun Ultima Weapon EX I got in late Shadowbringers where folks successfully blind-progged (almost) the entire fight. The only thing I did end up eventually having to point out was the Aetheroplasm debuff the tanks would accumulate; it's the first place I think there's a forced tank swap mechanic, and so they just weren't thinking to look at the slowly-accumulating debuff. When they went "Okay, we give up, what keeps killing the tanks?" that's when I pointed that bit out (and that even debuffs which a healer can't cleanse are worth looking at the tooltips for).
I always do stress to them that in the NA datacenters, extremes are usually done via pre-made parties in PF -- which gives you the freedom to pick how you want to approach the fight, and whether or not you want to try it blind -- and so on, and generally folks are receptive.
But if someone says "Yep, I read up on the mechanics," I admit I'd be shocked, because frankly the game gives them no reason I can think of to believe they should bother doing that before queuing into their first extremes.