Zen (Everything in this characters kit enables snipers)
Brigitte (repair pack is an excellent peel tool)
Ana (can hit them from range and enable kills)
Lucio (to an extent with his speed to help them move)
Baptiste (to prevent dives and add a field)
The sniper meta actually have a variant of the support line-up… wait for it… WITHOUT MERCY. So no. Despite your long reach into obscurity, Mercy doesn’t enable this meta. Damage creep, minimal ways for tanks to deal with ranged threats, and massive barrier nerfs is what enables with meta.
Mercy just benefits from it. Anyone with half a brain can see that snipers can roll without her.