The arena system is a joke. Sadly I doubt they'll change it even if it would be a conceptually easy fix - I would think a daily/monthly "tag" system would solve sniping (as mentioned recently by @medetec) and probably encourage more crystal spending but I guess they don't see it that way. Thankfully I'm getting close to maxing the available characters so in a month or three I can just ignore it save for when they add new farms.