Xeviat
Dungeon Mistress, she/her
I really like that idea.I'd just let any characters do something cool if they roll high enough, narrative-depending. Having these masteries implies that non-martial characters can't topple or push or graze, because if they did, that would be watering-down the class abilities of those who can.
Or like the abilities introduced back in 3e's Book of Nine Swords?
As for Book of Nine Swords, yeah, I'd love it if high level fighters could do legendary things.