I thought about adding aggressive and defensive stances as alternative martial arts.
Possibly some sort of charge/push style that lets you move even when blocked, by having knockback+step in attacks.
No stance+martial art combos, that sounds needlessly complex and not really a good addition. Martial arts should be the same thing as stances.
Also no ranged martial arts/stances, this sounds like a terrible misapplication of the system. Different ranged attack modes could exist and even be unlocked by skills, but they shouldn’t be mixed with melee martial arts, but rather use the same mechanism as switching between single fire and burst.
The idea of stance taking time to discourage switching doesn’t sound good. Switching between melee and ranged stances shouldn’t be a thing at all as they shouldn’t compete with each other, instead being totally separate.
Switching between melee stances could be a thing if they were balanced well enough that you’d WANT to switch them in the middle of combat. Otherwise it would not be useful for anything, since putting an emphasis on something already heavily encouraged is totally not needed.