Oversimplified Hitler's problem wasn't that he believed making Germany the best country he could, or that he thought it was the best place/culture. That jingoism is harmless and good for countries... to a point. Go Team America, Fuck Ya! Who cares if we cheer our team at the olympics, or take pride our accomplishments and strive to be better? That's not bad. If your national neighbors have 5x the murder rate and corruption, then you might want to filter which one of them you let in: for the same reasons you shouldn't let a Clinton or a Kennedy babysit your little girls.
Hitler's problems were that he was a progressive-collectivist-racist, who didn't believe in individuals over the state, and he excluded many citizens from being "true Germans". So that he could exclude 20th generation Jews as not being "true" Germans and treated them like sub-humans? Now that's a problem.
It's almost like when the far-left says all right wingers are Nazi's (and sees them everywhere), and then says/thinks, "punch a Nazi in the face" is a valid work view. Or when Black Lives Matters sees racism behind every badge (or in every white person who doesn't profess their privilege), and then thinks it's OK to be a bigot, vandal or assault people because of it. It's that blind, non-introspective hate, that scaled poorly in WWII Germany.
The other big problem is that Hitler wasn't a nationalist. If was a Nationalist, he wouldn't have wanted to leave his borders and invade. (He would be happy in his nation, with his people). The problem was that he believed in imperialism, and that he knew more than others, and could make the world a better place by telling others what to do. (Like all Socialists believe). So forcing his world view on others by force, that's a tenet required of Socialism -- but not of Nationalism.
Remember, if "that wasn't real Socialism" is the defense of every failed socialist country (like in the case of National Socialism), then that means, "that wasn't real Nationalism" is the obviously valid defense of National Socialism. Since America was probably most Nationalist before the progressives took over, and we went from being nationalist to being imperialists. Switzerland is one of the most nationalist countries in the world.
So that the Fascists (National Socialists) marched around singing nationalist (self-praising) songs, and showed their Hugo-boss pit-stains to each other? That was the least of their problems. The they were progressives, collectivists, Socialist, statists, totalitarians, authoritarians, or just plain so arrogant that they refused to look at the consequences of their own actions (like progressive leftists everywhere)? Now THAT was the problem.