Well (imo) an optimal line up has 1-2 healers. 3 is manageable depending on zone, but if you dont cap first you may have an extremely rough time re-taking the node.
But healing is never going to win a match, at best healing will be a stalemate and even in a stalemate I believe that kills are the determining factor.
Which is why you are seeing a lot of new strategies to start wzs. You dont just simply send 1 person to node and the rest to fight at mid. You have some going 4/0/4, 2/2/4, etc etc, because getting the first tick matters. Having strategy matters.
The problem is that most premades are cowardly and it's easy to come to the realization that if your guys aren't dying, you probably won't lose. Now, if you've 3 (or more) healers you're not going to have much DPS either, which means if the other side has any healing they also enjoy the same 'can't lose' advantage you have. And sure strategy matters but now a game of Alderaan would be like 'they got the first tick, so thanks for coming and DPS pretend you're trying to kill someone for the next 20 minutes." Is that really the kind of gameplay you want to encourage? Do you really want 3 DPS glue themselves to a node on Voidstar/Novare Coast and just cap nonstop from begining to end? It's a perfectly valid strategy in a heavy heal versus heavy heal situation, and you can even say good players will be better at chain capping (they presumably will know when is the best opportunity to do so and throw out CCs as necessary). Sure this is still a matter of skill, but it just feels weird to say our DPS was better at clicking the node than the other side which is why we won. Shouldn't we won because our DPS is actually better at killing their guys than their DPS?