you probably don’t want to make the third swing at -10.

This, and you should think about then when either creating the character, or at least when leveling up.
Any character has options to support others and can get new ones or improve those they have.

A minotaur like that sounds like great fun to play as, but also very much shoehorning the race in to martial and easily outperforming other ancestries there.
So I wonder what the cons are going to be.

Do all large creatures have reach in pf2e?

Other PCs riding them seems like it can be fun and worked with.

Yeah it would make no sense for either to be slower than a medium creature.
If anything, they should be faster.
But they should also have more hp, be stronger and such.

So I really wonder where the balance negatives would happen.

Maybe maluses to saves (not fortitude) or stats?