https://www.youtube.com/watch?v=oAp9vsC30gY&t=27m23s
Originally watching the video, I was under the impression he destroyed the entire capital ship.
Upon slowing the frames, it looks far more ambiguous.
Assuming the ship was mostly destroyed, then yeah, Plagueis is being vaporized.
If just a thin majority of the ship was destroyed, Tyth's still winning, but maybe not vaporization.
In the situation where just the front of the ship was split apart, then I guess it's possible Plagueis resists.
He'd be resisting via pure scaling, though. None of his feats compete with even splitting the head.
He blew the ship clean in two, destroying the front half, and he focused the entirety of his attack on the very tip. Effectively, he completely annihilated half the ship without even aiming for a spot suitable to do so.
Tbh, I still think that's grounds for him vaporizing Plagueis if that kind of power was focused on him alone.