It didn't.
Not only is it mathematically impossible there are German records talking bout the typhus outbreaks in the concentration camps.
If if the holocaust wasn't mathematically impossible, which it is, Mao killed more people during the great purge than died in all of WW2 and Stalin killed more people than the jews claim died in the Holocaust.
So if mass murder is what made Hitler the great evil than Stalin and Mao, by leaps and bounds, are the greater evils.