I keep hearing you either have evasion or MRR which isn't true. Evasion does nothing if you have a bad reflex save.

There are really three forms of magic mitigation

1) Improved Evasion (half damage on failed save, no damage when making a save)
2) Reflex save (full damage on a failed save, half damage when making a save or no damage when making a save with evasion)
3) MRR

There are cases where only MRR works. On a wizard I am likely to take insightful reflexes to boost my reflex save for magic mitigation and stay in a robe. On a warlock my reflex saves are much worse so I'll burn a feat for medium armor proficiency instead.

If you make your reflex save you are reducing most magic damage by 50% right from the start before MRR.

In general I think raising MRR cap is the wrong solution. If there are quests/raids where un-evadable damage one-shots people in robes that have a good reflex save - it's a design issue because monks can't be centered in anything else. If damage can be mitigated by MRR or reflex save - it's a player problem - you have to get more hp or invest in something.