The impact happened well after the formation and likely after the cooling, so the marks are unlikely to be from any rotational forces.

And some bodies—like Ceres and Pluto—are really only a trick of taxonomy away from being planets.

This misses the whole difference between these objects and the eight major bodies.

Ceres, Vesta, and Pluto could have ended up bigger or smaller, but still come from regions where material remained fragmented into hundreds or thousands of pieces. None of them were on their way to becoming anything like even Mercury or Mars, where almost everything available aggregated into a single body.

The result is a substantial difference; rocky Mercury is 25 times the mass of even Pluto, though that formed far enough out to collect ice, and some 360 times Ceres. And it’s not entirely random, since once Jupiter formed, it would have prevented the aggregation of another planet so close.

The solar system isn’t just a collection of random objects. Whatever you think of taxonomy, if you want to understand its structure, there’s a major split here to keep in mind. There could have been more planets, but Vesta was never going to be one.