By the way, "supremacist" in the way people like you use it is an anti-white slur anyways

If you think white people should rule over others, and actively seek to conquer them to rule over them that is what white supremacy means. There's nothing anti-white about that, if that's what you want then you're a white supremacist.

It's perfectly natural to want your race to have power, and among all other races people with strong ingroup preference hold "supremacist" attitudes (often far more extreme than those found among white nationalists), but somehow only whites are supposed to be pacifist isolationists and just let black and brown people dominate the world.

This is a ridiculous notion, there's no contradiction between having power and not being able to take over the world on a racial basis because you believe you deserve to rule them. Racial and ethnic nationalists believe in self determination as a rule. This has been the case for the 20th century form of revolutionary nationalisms and national liberation movements. The belief that white people have to go out and attempt to rule over foreigners is pretty niche and confined only to capitalism/liberalism/colonialism historically, even then it wasn't really racial or ethnic that was just happenstance; their real motivations were simply economic to feed the bankers funding the various European empires.

The non-racialist and non-JQ part of the alt-right was never truly part of the alt-right to begin with, that's the alt-lite and it emerged years after the alt-right itself emerged. A lot of "anti-SJWs" and other alt-liters turned alt-right though, as they watched the alt-lite get BTFO'd by the alt-right in debates (such as the famous Richard Spencer vs. Sargon debate). The alt-right itself was undeniably founded as an explicitly white nationalist movement, considering Jared Taylor, Richard Spencer and ironically enough also David Duke, key figures in the formation of the alt-right, were all explicitly pro-white.

From 2015-Charlottesville (If you look at the trends, the term only really became a popular thing in mid 2016) these people considered themselves alt right and the vast majority of people viewed them as fellow travelers, alt right roughly meant pro-Trump, Brexit, anti-SJW etc. Before then the alt right wasn't really even much to speak of, it was just a term Richard Spencer used for his website that hosted white nationalist content. The 'movement' only really started to refer to itself as alt right around the time of Trump and stuff. Before then most WNs would just call themselves that and the anti-sjw guys would call themselves rational skeptics and that kind of thing.

I agree they shouldn't have been considered one movement and it's absurd, but to say they weren't is just wrong.