Maybe. For me, I also feel like 3 is necessary @ flag groups, but for some reason (at least in Maelstrom), 2 is generally accepted and then people start to lose their s*** when an opposing party uses 3 or more healers. Majority of the time if I decide to be a 3rd healer pre-match's start, for some reason a lot of the time one of the other healers decides that's one too many and swaps to tank or DPS. But anyway, that's going on off on a tangent. I consider a 4th healer to be "stacking."

There are ways to "deal" with healer stacking, but they are not feasible for most randoms queueing with each other or without fairly specific set-ups or voice chat. The difference between the removal of Cleric Stance and Medica II + Regen losing stacking ability from different WHMs (in additions to something like a MND nerf for too many healers) is that the latter doesn't affect WHMs and SCHs as a job, but rather, certain set-ups. The "nerf" is pretty much nonexistent for parties who don't engage in those specific party compositions; much like parties that get slower LBs with too many of the same jobs.