Worth noting that if you make the leaver penalty much harsher, people would just disconnect at the start. So instead of them leaving and you being able to start looking for a replacement immediately, you're now forced to wait 5 minutes to vote kick then you can find a replacement.

Also, in the case of a tank/healer being the one vote kicked, the remaining healer/tank will very likely just leave as soon as the kick goes through and instantly requeue while the 2 DPS are stuck waiting for a tank and a healer.