Lemme tell you a little story. Yesterday, I joined a PF of people wanting to clear Garuda Ex. We eventually got a party with everyone agreeing to do the trial synced. Since we were all mentally prepared to do this and the newbies had done their homework, it was way easier to get the clear by explaining a few things here and there. Since we did great with Garuda (cleared it on first pull), we decided to do Titan next. A few hiccups here and there but we managed to clear. Ifrit was next and it was a bit more challenging than the other two. But with a few explanations here and there, some strategizing, and a bit of practice, we managed to clear. Those 3 fights were so fun to do. We were all doing our best and working together with no one slacking off or expecting a carry. Granted, I went as a healer to be able to save the runs as much as possible since I'm very familiar with those fights, but everyone else also did great.
Bottom line, Ex trials are better done with a group that's not forced to do them but rather chose to.
Mentoring in Ex fights doesn't mean to do all the work. I remember a discussion you were part of in the Tales from the Duty Finder thread. It was about tanks who don't even have the reflex to turn on their tank stance (even when aggro is clearly all over the place). This is the average experience in Mentor Roulette when it comes to Ex fights. People expect the fights to be a faceroll. You can't possibly tell me it's a mentor's job to put up with this. Besides, the logic of "You don't want to get an Ex trial? Don't queue for Mentor Roulette" is just so bad/flawed and short-sighted. Mentors in different other content can be such an asset if only by filling up the queues for older content, yet by this logic, we lose this advantage because of something like Ex trials. Throwing away a whole batch of good fruit because of 1 rotten fruit (Ex trials) doesn't sound too smart to me.