The problem is that you are all stuck looking at enmity. The problem is rather that you can pick an awesome DD and just spam heal it and it will tank. This is what needs changing. You shouldn't be able to deal best damage in the game and live just because you got a healer in the party.

Best damage = death. Should be the rule rather than the exception. DDs should be forced to wear "survival" gear if they want to go all out, instead of just wear full DD gear. Basically you have to dress like a PLD if you want to live, else you'll die.

Easiest way to fix this would be HP adjustments. Lets say a PLD has 2k HP, and a WAR 1k HP. The WAR is much more likely to die than the PLD. But of course WARs should be able to tank also, so they could have Defender give like 500 extra HP for 20 minutes or something, making you better at tanking, at the cost of attack.