Muramasa/Foil are great for questing as long as you are fighting stuff that does not hit too hard or live too long. Sometimes you need that extra buffer to stop your guys getting 1 shot, or that extra bit of recovery to keep up with the pounding you are taking.Do you find that muramasa and foil are useless for questing/vortex? I basically don't change anything out. Currently my team has 1x foil, 2x muramasa, and 2x stat booster.
If I used the same team for arena and questing I'd probably not bother to change them except for trying hard stuff. My main team is an absolutely terrible arena team though, so I keep em separate.