Instead of defeating other players being worth no XP, use the following guidelines. Player level is the same as used to determine the leading player in the endgame rules, etc..

Player defeats a lower level player = 1xp

Player defeats an equal level player = 2xp

Player defeats a higher level player = 3xp

Just an idea to make PvP more appealing. As it is there isn't a whole lot of motivation to fight other players except to steal Runes toward the end of the game.