>>12257089I mean, that's true, and leftovers help, but I think it's also just because Blissey has been a mainstay since Gen II.
Remember tiers are a popularity contest. Evio Chansey is clearly too powerful for UU, she's just used marginally less than Blissey. It's not a question of viability so much as popularity and I think the relative newness of Evio-driven builds is part of that.