Is that feat of regenerating from a stab wound really Low-Mid? That requires severe organ damage. It seems more like Mid-Low for regenerating deep wounds.
Either way, Buffy is a master of numerous martial arts and has years of experience against enemies comparable to herself and against groups, with even standard vampires generally having at least decent skill. She's a match for Angel, Spike and Dracula who are centuries old and have lots of their own battle experiences unique to them, a match for Faith and Kendra who are themselves highly skilled Slayers, superior to the Initiative's soldiers including Riley who is effectively special forces, and her skill list goes on and on.
She-Hulk meanwhile is less skilled than the average vampires Buffy fights groups of on the regular. In fact, she's less skilled than the character who basically exists to be a loser, Xander. This skill gap is positively massive.