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.