The thought occurs that if the tanks armor was good enough to ignore auto attack damage like water of a ducks back, and was able to absorb/mitigate more special attack damage, then tanks would really be tanks and healers could spend less time focusing on maintaining the tank during normal action. On the flip side, if DPS were receiving incoming damage from auto attacks and skills, they would need more attention from the healer.
This would put much more pressure on tanks to maintain crowd control, and make healing much more variable - and require more attention.
But for this to happen, there would need to be a few more adds/trash mobs, tanks would have to have a bit more in the way of crowd control skill and tank armor would need to be buffed vs ordinary weapon-skills and auto-attacks. There would no doubt be complaints about tanks being so 'tanky'. To be fair to all, this would be something that happens in a party only - basically when the tank has someone to protect, their defensive abilities should be come sharper, just as a healer should become stronger at heals and DDs should be just that bit more lethal. In other words, during party content our respective roles should be stronger than they are in solo content.
So, let's see, plucking numbers from mid-air, during light /full party content a tank's DEF scores should be +20%, Healers heal potency should be +20% and DDs output should be +20%. This would really focus people's attention on their roles, healers would need to focus more on actually healing and removing debuffs, tanks would focus more on crowd control and their tank stance to protect DDs and healers, and DDs would be the undisputed kinds of offense with the obvious responsibility of killing things, but their increased damage while partied would mean tanks have to remain in tank stance much more to maintain proper control... Strengthen the main aspects of each role in the trinity, rather than blurring the lines. This will make it easier for players who want to heal to do just that and perhaps make the role both clearer and more attractive.