It's not a partisan point at all, it's an observation about how immigration and changes in the polity interacts with politics. Left-wing parties rely on immigrants for votes all over the developed world. And the larger topic of how foreigners influence a democratic system is one Aristotle was writing about even in 350 BC.
> do your part by working to adopt our culture rather than proudly championing the exact zero-sum politics you're bemoaning
You should read up on game theory. It doesn't matter what I do, the millions of other immigrants that come to the U.S. will change its culture to be more like their homelands'. Your only choice is whether you want the left-wing version of those countries' politics, or the right-wing version? Both result in fiscal disaster, followed by an Argentina-style correction. (We should be so lucky--Javier Milei seems to be doing a pretty good job.)