Valygar is a fantastic NPC, in my opinion. You're kill stats sound a little off...was he petrified or did you dump him from your group? Just some ideas...
I have him dual wielding the Celestial Fury and his own family Katana, + he has the girdle of Stone (?) Giant Strength (the st:21 one) equipped, so he's an absolute tank against all! His own family katana does not backstab, so I put that in his offhand, and the Celestial Fury in his weapon hand.
Tanith.