Originally Posted by Fat Shokwav
I don't really know if Regenerator is the main factor (Mienshao is Fighting-type and resists SR, but it's UU)
It's a major one, but not the main one.
There's still so much to Tornadus-T, that stripping one of them (whether it's U-Turn, His flying typing, Superpower, or regen, or the simple support known as drizzle
) would make him more balanced for the tier. So much power and versatility with so little support needed calls for a change.