Just because you weaken two AoE heals on each other doesn’t mean they don’t work together. Nor am I asking for 2-2-2, as I said above, it isn’t the way to go.
As for AoE heal stacking, this would only affect Lucio and Brig together. That’s it. And Zen if he ults because then Lucio and Brig would do 0 healing to targets in Trans. That’s it.
Mercy would still pair with Zen because neither heals are AoE (outside of Valk, so Valk would take president over Lucio’s amp for example, but not Mercy’s standard healing. Those would still stack).
I’m just offering a solution outside of implementing anything else into the game that better soft counters than what we already have.
I’m perfectly okay with never implementing that AoE heal thing if there is a way to reduce the synergy of goats without it. It’s just one idea of hundreds.