It could be as simple as increasing the potency of mitigation on tanks as well as the amount of damage enemies do. it wouldn't be overly complicated either.
the issue with mitigation is it's weak and unnoticeable in most cases. and part of that is that also down to the incoming damage overall. when a tank can spend most of there time in dps stance because they are taking nextto no damage. using rampart to mitigate 20% of that almost neglible damage makes an unnoticeable amount of difference.. in most content a tank could run through without a single cooldown and it wouldn't make a real difference at all as to how much healing was required.
They could make a huge boost to the potency of mitigation cooldowns and add a huge buff to the damage enemies do. if enemies hit for like double there current damage but rampart mitigated say 50% of that for 20 seconds, you create a scenario where there becomes a noticeable difference between tanks that use mitigation effectively and tanks that don't bother and also increase the overall importance of healing. the problem that exists at the moment as far as tanks go is mitigation doesn't realy matter or make a difference the damage the y take is so laughable they can literally pull every single mob in a dungeon and / or spend most of there time in a dps stance. and its the same for healers.
a scholars sacred soil for example is never going to save the group from a massive incoming damage spike or bosses ultimate attack, only 2 things happen here.
1 the group clears the dps check which results in the incoming damage being next to nothing and the group sails through with ease. in which case using defensive buffs is often laughable because the bosses ultimate will hardly scratch the parties hp pools so mitigating 10% of nothing ultimately is nothing.
2 the group fails the dps check which results in an instant wipe and no amount of defencive buffs or healing will save you.. sacred soil divine viel fey covenant succor and stoneskin, you're still gonna wipe.
from a healers perspective or at least my scholars for example another reason I say mitigation is laughable Is because it doesn't change very much.
if a tank eats 15k damage and mitigates none of it. 1 of my psyckiks isn't enough to heal him. but 2 ends up with the tank being overhealed
if that tank ate that same 15k attack and mitigated 20% of it with a cooldown. it wouldn't change. 1 of my psykiks wouldn't be enough to heal him. but 2 would result in overheal. and its because of this that the mitigation goes completely unnoticed and is often irrellivent. the amount of healing required is no different whether a cool down is used or not.
this is why I think they need to move away from being so dps orinentated and make mitigation and healing more important.