Hi there,
I personally think that XP should remain from playing games. Like previously mentioned, it motivates players to play the game and actually to try to win. For example, someone might join heaps of matches and just stand around for a while and then get eliminated, but someone else may play only a a few matches but win every one, but wouldn’t have gained as much XP than the other player did, which would be unfair.
There may also be some issues of players being AFK. It does kick you out of the server for a while of being AFK, but every now and then the player can just move one step to reset the AFK timer. Someone could just be doing that all day everyday and getting higher up in the rankings without even doing well in a match.
Anyway, XP should be there to motivate players to keep competing, not to keep joining. But thanks for your suggestion :).