One way to fix this is to split Feast from the other PVP modes. As a single healer (SCH experience) in Feast it goes wrong very quickly if over tasked. The recent nerf to Chain Strategem has been surprisingly 'effective' in cutting SCH DPS utility, in my experience.

In Frontlines if there's a team with 3 healers (especially in Shatter) then you cannot take anyone down, especially their healers. Last night in a 24 man Shatter our entire "alliance" of 8 (standard 2-2-4 composition) couldn't take down a focused single member of the team with three healers. The healing & shielding power was just far too much. The rest of their team just hammered the ice. If we focused on ice instead their team would just cc us or pick off a target.

So yes, in certain situations healers are overpowered in PVP. A quick & ugly solution would be to have a system to prevent more than two healers per team. That would prevent the need for further mutilation of healing abilities.