You're missing the point of the ability.
It's not a unique individual heal you're meant to throw by itself. It's a topper for the most part. Something you throw for free at the tail end of another ability to get you that last bit of HP you need.
For example, in O2S coaching a group with a SCH, we quickly settled on Medica II + PI + Indom to deal with the first aoe, that combo had us topped enough thanks to the PI to safely do the stack mechanic that follows. Without PI I'd have had to throw another medica at the expense of my own DPS and MP.
For the most part, it's best to think of it as a 1 minute CD that lets you throw a 700 potency cure 3, or a medica II with 350 potency upfront. In that regard it's actually more potent than Largesse.
The only occasion I've consistently seen 3 stacks is in the final phase of O3S (and ofc the later stages of O4S). Outside of there it's just not worth chasing multiple stacks as you won't see them unless things are going wrong.
TLDR, it's not a cure 3 or assize in it's own right, use it on the tail of an aoe heal to top people when you need that little bit of extra aoe burst but don't/can't use largesse.