Look at it this way; if the team has a bad tank that doesn't TBN the teammate that is currently being focused but the healer is on top of their game then the team still has a chance to win. If a dps is still learning or is not damaging players as much as the other dps on their team but the tank & healer is able to put on some damage they can still win. If a healer is not that good or learning the other three members can't do anything to make up for the skill gap in the role of heal and they have very little chance of winning the match. While a straight nerf to healer is not a good idea, some changes to all the roles are needed to put more of the deciding factor into the team as a whole instead of being too much on one person knowing how to heal. Allow tanks for a off-heal CD they can put, dps have a heal oh shit button, while adjusting the healer so that the other team members will need to use them perhaps.