its like, no matter how bad the vi is.

This is true. Proven by the 100% vi pick rate by pro teams at last years worlds, oh wait...

you say that like there's absolutely no counterplay

Riot is adding more and more counter play mechanics for abilities such as that. For example tahm kench devour ability. As well as other older abilities like any displacement abilities to knock her or any follow up away after the ultimate has landed like a lee sin kick or janna ultimate.

Vi actually isn't as easy as you suggest and nor is she OP by any measure. Vi is dependent on landing Q early on and if she misses that even later a lot of her damage is lost. Moreover, she needs to cancel autos correctly etc. I think compared to many junglers, she is of average difficulty.