I think having being "The Slayer" should apply as the toughness catch no a number of Buffyverse creatures.
It usually doesn't, actually. For opponents with unique defenses, she typically requires unique solutions. One vampire with too much Toughness to be staked gets hit with a sharpened post or something. An ancient demon immune to mortal weapons turns out to be mostly just immune to Weapon:3 and below, not so much rocket launchers. The She-Mantis gets owned with bat sonar. Et cetera.
Her being the Slayer puts her on the same level as most of the things she fights, and her living on the Hellmouth puts her in the same territory. Beyond that she mostly has to do things the hard way, and it's notable that Buffy's unique longevity and efficacy are due to the friends she makes (mostly Willow, let's be honest). Most Slayers burn out and die quickly.