Vercel is big enough and important enough that such a reader will undoubtedly know of it. That reader will probably, but not certainly, also know about eleventy.
Netlify, who arguably started or at least encouraged the space Vercel inhabits, is understandably pissed that they aren't in Vercel's shoes today. Eleventy is pissed that they are receiving a bit of collateral damage in that messaging war.
Vercel and Netlify offer essentially the same thing: easy hosting of mostly static websites + a few bells and whistles. They each support development of frameworks (eleventy, Next.js, Gatsby, and perhaps others) that make their hosting business more compelling to use. Netlify branded it's approach as "Jamstack" which I believe stood for "Javascript and some other Marketing Stuff". Now that the winds of change are blowing, Netlify want to reposition themselves as something a bit different and down play the old stuff and also not make it look like their rivals are doing to well.
Although the features can work without Vercel, it's a second class citizen.
The more popular Next is, the less reason people would choose netlify over nextjs as a default option.
So there is frustration that the React project is now perhaps an extension of Vercel's interests, and focused on helping them sell hosting.
Never ending drama in VC land.
It was my (perhaps outdated) experience that in fact some elements of JS (like using scraper libraries) would not work on Vercel at the time due to memory of serverless function and other limits. But locally they worked on my dev machine.