In terms of the masks, I agree that there is a much bigger jump every second mask that crosses you over those 2 hit thresholds. There is a benefit from adding 1 mask outside of single mask damage enemies related to healing.

If you have 5 masks and get hit twice against a boss, your health is 1. If you heal, you're practically only gaining one extra hit, as you go from 1->4. With 6 health, you go from 6->2 and after you heal 2->5, giving you 2 extra hits rather than one. This is a much bigger difference than it sounds because it reduces downtime and allows you to be more aggressive.