The biggest mistake Hitler made was holocausting the jews.
Aside from that, dude had a way with words and could work a crowd like nobody's business. His speechs would get someone elected in any western country.
he should have just ruled germany, retired, and wrote a "how to" book on delivering speeches and ascending to power. That would make him a celebrity.
In some parallel universe Who knows? maybe hitler could have starred in a painting show on PBS. That would give him an outlet for his art. Maybe instead of Bob Ross, Hitler could have been the beloved cultural treasure. Maybe in that universe, Bob Ross is the mass murdering fascist with the God Complex. You never know...
