Why is it weird? It's what would happen.
If a healer is going to do more dps than a tank if optimised (as proposed by the other poster) Then the name of the game for tanks is minimising the need for a healer.
That is unfortunately going to be the only deciding factor as to why you pick a tank.
Either way, you already know my stance. If this were to ever happen, be happy. But i'll *REFUSE* to tank for you.