Hmm..while I understand the complaint, I have to call the question the necessity to fix it. The only thing 'heal tagging' can get in the way of is mob drops. People can still get hunting log credit, experience credit, and quest credit regardless of the state of the mob. Even quest item drops from mobs will happen regardless of claim state (though I believe you still need to deal a third of the mob's health).

As far as open world mobs go, people are likely farming them for something other than exp; as that would be a sub-optimal approach to leveling. For the specific exp gains on a claimed mob though... I believe it is based on the percentage of damage dealt beyond 30%. So if you are leaving mobs at 100% health but claimed due to cures or regen, then the players killing the mobs are still receiving full credit or near full credit. But even if not, they could always be getting bonus exp based on exp chains they're on.

That leaves the main issue of item farming. If it is a highly contested area for mob drops, people are already blowing instant casts and AoEs to claim mobs anyway. Accidental claim is minimized thanks to this. To me, it is highly unlikely a cure or regen tick will interfere with them.

So all in all, considering the FFXIV ARR content of FATES, Dungeons, Leves, Quests, Hunting Logs, and Open-World Grinding... Heal Tagging only applies to one very small, very specialized instance of interference. Other than that, heal people all you like, knowing you are helping them survive encounters. And relax knowing that their exp is hardly marginalized, and that you are not interfering by accidental claims.