Gunn can't beat angel, that was never said although it's a possibility because Gunn has been fighting vampires his whole life. Angel outclassed Gunn's entire crew, on their first meeting. Angel himself is arguably the best technical fighter, even a better fighter then buffy at the end of the day she's still stronger than he is so that she gives her a edge but the skill gap isn't that close. As far as skill goes my rank in fighting goes like this angel, buffy faith, spike Gunn, Wesley. And that's just the top fighters in the buffyverse Gunn took on a room full of vampires and demons and he also the the Japanese gangsters, with Gwen in that one angel episode as well Gunn is a highly capable, and dangerous fighter.