tbk isnt a heal or supiror to it, its because tbk only lasts for 5 seconds while actual healing isnt on the clock

this means unless an enemy is dealing over the 20% within that 5sec window it isnt getting full value while pld could heal over 20% of his own hp and have that hp when he needs to take the damage, this also in turn saves the healers time to heal and allows them to do more dmg instead

honestly not sure why drk didnt get a proper self heal this expansion, tbk is nice but it certainly isnt a heal, just more mitigation.