Actually that's pretty much the bare minimum needed to make Coil tolerable. Many people don't go in until they have a couple of Myth pieces even.
You can clear Turn 1 with one class, then go in on another for Turn 2 if you want, assuming it's geared enough for that content. You just can't go back to Turn 1 that week on a different class for a chance for loot for that class.
They've also made Crystal Tower, which has worse gear than Coil, have a one week lockout timer on getting loot regardless of your class, but you can still run it as much as you want to help out people and get philo/myth I assume.
