There's "HTML" and then there's the kind of website where the final DOM isn't known until the user has already been attempting to read it for 10 seconds. There is a substantial difference in the % of browser capabilities that need to be exercised between the extremes of use.
Complexity of implementation is what ultimately separates the good from the bad. Any tool can be operated skillfully or poorly. An apprentice with a circular saw and a fully charged battery can do a hell of a lot of damage. A master may elect to use no tool at all and simply bang on the side of the thing (I.e. push back on the business).
The latest websites I have built are some of my most compatible ever. I don't use web sockets anymore. I don't depend on JavaScript to have piecemeal conversation with the server. You can actually use ~80% of the product with JavaScript entirely disabled. How are the engineering choices demonstrated here not exactly the solution for walled garden lock-in?