Multishot doesn't deal more damage when more than one arrow hit a mob at once

I think I know why this happens, and it's really annoying. Minecraft has an invincibility cool down when enteties are attacked, This can easily be fixed, as servers do it all the time. This would help fix a lot of other problems, like that one time I should have died from fall damage but got hit by a fireball last half second before collision with the ground