They might've done it to open her up to be played alongside heroes that heal less. Could we do zen + mercy before? Yes but there might be frustration with that combo.

Mostly I think they wanted to shift the power from one part of the kit to the other rather than straight nerfs like they did with sombra.

Theoretically I see what they tried to do, but it remains to be seen how well it works out. The meta changes and people still get used to it. They also forget that mercy doesnt always have to rely on her passive to heal because her other can sometimes heal her as well. So not sure how things will look. I do think fhe other support needs to adjust to pay attention to her more.

I dont think I ever bothered to look up unless our mercy was burning from damage boosted dynamite. She was too self sufficient compared to other except lucio maybe. Now I plug heals onto them.