I understand this is intended for new players, but it's a roulette with only 2 dungeons in it, so it's 50/50.
My suggestion is, put storyline Primal fights into Main Scenario roulette e.g. Shiva, Ravana, Bismarck etc, and make Trial Roulette only have side-quest Primals like Hard Mode fights, Gilgamesh, Ultros, Odin, etc.
It's really boring that Main Scenario roulette is only 2 missions, not much of a 'roulette' if there's only 2 choices.