2000 potency is not a lot for a whole fight though.
+ as you said Lady was probably designed with this usage in mind: being able to use it instead of a GCD heal. Which means that in theory it is DPS neutral.

So, yeah, in dungeons it is certainly a DPS loss due to RNG. On boss fights, maybe not.
It's again one of those things that depend on fight design. If lilybell is any indication, I am hoping there will be more raid wide damages.