About conqueror sustain part

Since it heal the same amount of dmg of the true dmg. Does this mean that aoe spell heal for 10% of his actual value? Usually spell vamp or omnivamp heal less from aoe spell (only 33% total) but since in this case the same amount of true dmg heal, does this mean that we get 10% omni vamp on aoe spell that is also not reduced by armor/mr? Usually omni vamp and spell vamp heal from total dmg dealt so it's reduced by armor/mr (if the damage it's not true). In this case since the true dmg is converted, this mean that it's 10% omni vamp against all class meaning that the more the armor/mr you have, the more effective this rune is. Are we back into drain tank meta?