Taking your points in reverse order:
Yes, it doesn't make an argument. It doesn't hold itself out as an argument, but as a narrative relating of personal experience and recommendation of how to address similar experiences. Not every piece of human communication is or needs to be an argument.
Is it pretentious? Maybe; I mean, it clearly engages in what it belatedly admits is a potentially overgeneralization of personal experience, and one could view from overweighting one's own experience as pretentious.
But...whatever. It does, even if it is at the very end, acknowledge the issue.
> The strawman they propose is just one argument, and is not the one I would reach for when arguing against Racket in CS1
Presumably, you are not one of the author’s colleagues at Northeastern; also, Racket is only used in HtDP in the sense that the student languages are themselves implemented in Racket; each is its own distinct Racket/Scheme-like language, but is neither Racket nor Scheme.
Also, it doesn'tt address a single objection to the HtDP pedagogical approach, but several which it views as having a common underlying motivation.
> I am open to being persuaded about these silly language wars
While there are suggestions in the article for dealing with resistance to the HtDP method, those suggestions (and most of the objections they address) are not language wars, or even language-based. If you were open to being persuaded, you would probably at least have read closely enough to recognize that.
> but the argument there is completely uncompelling
There is not even an argument being made; it's advice on how to mollify certain objections, not an argument aimed at rebutting them. The audience isn't people that need to be convinced that HtDP is a good approach, and what it presents also isn't an argument to be used on resistors. It assumes that the audience is not only already convinced, but in also in a position (as the author was during the experience motivating this) where they don't need to convince resistors by argument, but where they are free enough that they can mollify them with accommodations and while proving the value of the mechanism by experience in action.
And even Felleisen's HtDP course isn't taught in Racket: it's taught in a sequence of "student languages".
EDIT: Some of this is mentioned on these pages, but not explained very well if you hadn't heard of HtDP. See some of the better links that other commenters have posted.