The question we should be asking isn't necessarily "how much better would we be with someone else" but rather "would we even be in this position with someone else?"
Pardew isn't perfect but he has his strengths and most importantly, he's the right fit for the club. Sometimes fit is more important than ability.
There is no doubt in my mind that Kevin Keegan is a tactically superior manager, but he was the wrong fit. Look how that turned out.