in advocating for ultranationalism within imperialist countries, they are passively also supporting imperialism. There’s a contradiction at play between their anti-imperialism and their ultranationalism, which was the point I tried to highlight.

I don’t know that I would use the term “ultranationalism” because that term has a more specific meaning that is not just “strong patriotism”, but yes, this is correct. That is exactly the problem with “patriotism” in the imperial core. This is what I also pointed out in my other comment:

The distinction that needs to be made here is what that patriotism is directed at. In the imperial core patriotism is most likely reactionary, especially so in settler colonies like the US, because it protects a reactionary state formation.

It’s not the patriotism itself, it’s what you’re patriotic for: a reactionary, imperialist, settler-colony that exists on stolen land.

not to mention the incorrect analysis leading to the petite bourgeois focus.

Yes. This is, I think, the proper Marxist critique of their position that we should be focusing on (as well as their reactionary position on social issues and the national question) because it is a glaring contradiction with the Leninist ideas that they claim to support. Lenin was very explicit about pointing out how small-producer economic relations reinforce capitalism and lead to bourgeois thinking.