For something that is supposed to be dispelling myths, this sure has a lot of misinformation.
(1) First of all, not all white supremacists identify with "Anglo-Saxons", which you seem also to misplace. See: https://en.wikipedia.org/wiki/Anglo-Saxons
If you are just using "Anglo-Saxon" to mean vaguely what "Aryan" meant, well, Western Civilization is complicated. You really need to unpack it a lot more (and also you completely neglected the substantial Islamic influence, both in original intellectual contributions and keeping alive knowledge discovered by the Greeks and Romans). But to underestimate the historical impact of Northern Europe in the Enlightenment and development of the scientific method is folly--there were immense and profound contributions there, built on top of immense and profound contributions throughout history. Saying that "Anglo-Saxons" did nothing is completely misleading at best and flat-out wrong at worst. Humans are excellent at building upon their best ideas.
(2) Your logic doesn't hold at all. We don't treat sheep with the same respect as people; we hold them in pens, slaughter them for food. Obviously this is because we are secretly afraid that they are superior to us?! Not at all!
You correctly identify the belief, and you correctly indicate that it is wrong, but your reasoning completely doesn't follow.
Why not use the actual reasons that they're wrong, e.g. (1) that careful studies trying to account for different factors do not show a significant difference between racial groups, at least not within the uncertainties, and/or (2) even if one group on average was better or worse than another at something (even if it's IQ!), it is antithetical to modern ideas of liberalism and human rights to treat people poorly or limit their opportunities because someone else who you've put into the same bin doesn't measure up to some threshold you've selected. So it's wrong because it's wrong biologically, and it's wrong because it's wrong ethically.
(Caveat: it's really hard to do a proper controlled study where you keep everything the same except "race" (however you divide that), so our accuracy in measuring and contrasting things across "race" is not very good. If anyone tells you--as many people like to--that science has "proven" that there is "no difference"...well, no, that's not how it works. Rather, it's more like "we have high confidence that the average difference between groups, if given identical conditions, would fall in a small interval about zero; in particular, we do not have strong evidence that it is not zero". Obviously for some things like resistance to ultraviolet light there IS a big difference, but for the big ones that white supremacists talk about like IQ and propensity to violence, the confidence intervals in the best studies (with relatively small confidence intervals) generally include zero. Also, it's really dangerous to try to do any research on this, because if you really accurately measure "very close to zero", the white supremacists will come after you; but if you measure "small but not zero", whoever is on the "bad" end will come after you. Kind of a no-win situation. And, consequently, the confidence intervals are larger than we'd like.)
(3) I am not familiar enough with white supremacist thinking to know anything about what they think about Jews.
(4) They actually did mostly build this country. The initial settlers were ill-prepared and benefitted somewhat from Native American help, but if the first ones had died, following ones would have succeeded. They imported their animals, agriculture, and technology, supplanting rather than adopting Native American lifestyles and crops (with a few important exceptions, but they'd have done fine without the exceptions). Slaves were very important to agriculture in the south, but there were plenty of farmers in the north who did just fine (and produced adequate crops to feed people in the north beyond themselves) without any slavery. The use of people of other groups was not out of necessity, just convenience (and greed), and even accounting for what wasn't produced by them, they still have the greatest claim to having built the country.
However, so what? The country was built around the principle that all men were created equal. Well then. Nice country! It's for everyone. Too bad, white supremacists! The people who built the country didn't build it to cater to your kind of hatred...and to the extent that they did, we follow their best principles, not their worst impulses.
(5) Yeah, the extermination thing is kind of silly. To be fair, there is a nonzero but small amount of weird fringe rhetoric about actually "exterminating" (diluting) whites--good luck figuring out who that even is--and a lot more less fringe rhetoric about exterminating "whiteness" which somehow has come to mean all sorts of hateful behavior, not a straightforward description of a skin phenotype. But, yep, I agree--it's popular among every radical or cult-like group to endorse the idea that they're under threat, and white supremacists certainly do do that.
Anyway, maybe well-intentioned, but this is bad enough that it's liable to be actively harmful if many people notice...because white supremacists love more than anything to find people who say wrong things about them because then they have a way to PROVE that the others are wrong. (And, of course, if opponents are wrong about one thing, even the reasoning to know that that one thing is the way they say, they must be wrong about everything.)