I get that asking a commercial website to be as basic/supported as that website is a big ask. I don’t think the other commenter was saying that such websites should reach 100%, only that they should start from there and sacrifice only as much as is necessary.
The trick isn't to get a commercial website to accept a site that basic, it's to get the website to test for capabilities and if it can't confirm them serve only the basic version. Websites should be every bit as fancy and obnoxious as they want as long as they fail gracefully.
In the real world that means there is a list of browsers and versions tested on.
Yes that is the fallback. That doesn't make it a bad example. Your core functionality should work on almost everything even if it's laid out a bit weird and missing niceties.
So: not bad faith and your accusation is unreasonable