Well, I disagree. "Belkar stabs someone" is merely the common element in a great many different hilarious situations.Belkar, on the other hand, is just stabbity-stabbity-stab. It really get old, at least for me.
"Got it out for you."
Also, Xykon's evilness is not as funny because he's the villain. Sure, the nonchalance with which he goes about it is mildly funny, but the whole "foil" aspect of Belkar is lacking.
The "bad guys" equivalent of Belkar would be the... is there an official term... unknown Monster.