I'm aware of the mend trait I just think removing the potency and making it a percentage based heal is better. Something like restores 80% of hp, if target is tank role it's lowered down to 60%.
I prefer paladin having DV having a heal only if it forced the player to lose out on attacking. If it turned into a spell you have to cast or at least a GCD I'd be more okay with it. If paladin became the support tank that would be cool, having it sacrifice it's dps and resources for its own sustain to support others is cool. I'd just want any form of healing that comes out of it to be something you lose damage for maybe even it's defensive resources like the oath bar for DV. Making it sacrifice it's own safety for others is very in theme and I would love that for paladin.
Tanks having healing is an issue if there's no sacrifices for it. Shake it off having a regen is dumb because it's an oGCD, if warrior had to sacrifice it's raging tempest buff to use it then maybe it could be more balanced.
For a bit of fun how I would structure the identies for each tank, mitigation wise at least is like this:
WAR = Life steal, nerf it's self healing in aoe, lower it's HP way more than other tanks, remove counterattack from vengeance, have raw instinct at level 30. Make it's entirely based around being a selfish lifesteal healer that's constantly fighting.
PLD = Support tank, sacrifices it's DPS and personal mitigation to support everyone. Mitigation self mitigation is strong but requires healers. Remove all heals off of magic attacks. Instead give it the more HP.
GNB = barrier tank, keep it relatively the same but add a trait onto it's cartridge abilities give barriers each time it's used. Has the ability to share this barrier with others like it's own deployment tactics.
DRK = revenge tank, make it have the best DPS again, give it's long Def cd the counter attack from vengeance, it getting hit fills the blood bar instead of its combo, mana management becomes a balancing act again and the hp sacrifice for MP is brought back. Killing enemies restores hp in dungeon scenarios.
This is how I'd approach it at least. But the tank I play is PLD so I'm not as engrained with the culture around GBK and DRK.