We definitely use incoming damage as a tuning mechanism

We definitely use incoming damage as a tuning mechanism, but we also use berserk timers to set a high bar for the DPS specs. There is a risk that if berserk timers are too tightly tuned that raids may attempt to replace healers with more DPS, which isn’t doing the healers any favors either. Note that limiting dispels to healers isn’t just a PvP balance issue. We wanted to know for sure that every 5-player group would be able to dispel magic. The alternatives were that there could never be important debuffs to dispel or some healers just wouldn’t be viable for some content.