Overall, having Ex primals isn't too much of a bad thing in my opinion. These fights are all exceptionally well designed and it's really a shame that they can all be blitzed through unsynced now. Are you expecting to always get a clear? Of course not, but with every wipe and fail you're helping the newer players understand the mechanics and get used to strategies they will need to learn for future fights - which is basically the point of Mentor roulette, and being a Mentor.
I had Titan extreme the other day for my mentor roulette, and after literally 40 minutes of wiping, we managed to clear and it was SUCH a great feeling. Not only for the people who cleared, but also for me being able to guide them through it and experience a fight I used to love properly (Without just unsyncing and beating him up in a couple of minutes). I could have just left as soon as I entered with the thought that it was hopeless -- but we did it and people learned!
All I can say is to just try your best to teach people and help them - don't always expect the clear, and just enjoy taking part in content that you'll otherwise never experience again.