Alistar Trample Stacks - 1 per champion hit per tick?

As it stands, Alistar's Trample ability only gives stacks when it damages at least one enemy champion. However, these stacks do not charge up faster when Alistar is damaging more than one enemy champion per tick.

What if Alistar gained 1 Trample stack per enemy champion hit per tick? Would he be too overpowered or reliable?