I'd say maybe. The thing with the Illyria/Siphon fight was Illyria tends to fight stupidly. It was the same deal as the Illyria/Hamilton fight, even though she as good technique, she usually relies on her sheer power. When she doesn't have a significant strength advantage, she almost always loses.
I would say Buffy & Angelus are two of the smarter fighters who normally seem to do well even when they're physically outmatched. Look at the Beast fights. Angel was torn apart by the Beast, where Angelus used his speed and tactic to fair well against him.
I would say that considering Pearl & Nash clearly outmatch Slayers or Vampires by miles--they currently have Superman-esque powers, and those guys are scared of Whistler show that he's going to be terrifying when he gets into a real fight.
To Glory, I would say all she had was her speed really. Otherwise, she never demonstrated strength any greater than Shajhan, the Beast, or Jasmine. I could even argue that the Master was stronger than Glory, as Darla was arguably stronger than Buffy, yet Big Bad vamps like Angelus & Darla feared the Master.