I think you are misunderstanding my point.
An img tag doesn't work on an AMP page. It has to be an amp-img. Every standard HTML tag is invalid in AMP content, as you must use a customized AMP flavor of HTML.
Whether or not it returns valid as HTML markup isn't really relevant: The point is it's an entirely different, incompatible, markup, from what a normal browser knows how to interpret and use, and if your browser doesn't have JavaScript, it's not even going to know what any of those custom tags are, is it?