Good point. It would also have synergies with cards that have a certain effect based on how much damage was dealt to a creature, albeit those are yet to come.
Still, in 98% of the time, a 3/4 Zombie with this passive will be the same as a 3/8 Zombie without, so my opinion is still the one stated above.
One more thing by the way, the damage would often have to be rounded up or down which I would also see as an undesired thing in card design.