No matter the validity of his ideologies, Hitler was responsible for the death of millions of people. So he's no hero
The history book would have been totally different if Germany and it's allies had won the second world. No one would have known about the Jews holocaust at all and they would have been very close to extinction.
You are right. The history books would have been different. But, what if the NAZI's had won and they just normalized the extermination of all non Aryans? I believe that is ultimately what they wanted.