Well I think the best method to slow down fates is just simply to make it so you do not gain contribution based on your party. So if you only cast a few spells it means you won't get gold, meaning less exp overall without changing the overall ethic of FATES. After all FATES on there own are not a problem, its 3x full parties milking it so hard. With less contribution it means it won't be the go-to and people will actually have to spread out a little. Shock horror they might even go to Outer Lasnoca!