Same. This is mind-blowing! And just goes to show how different “markup” is meant to be from “formatting.” Not that you’d know it when so much content is made by people using a WYSIWYG editor that basically tells them “you are doing formatting.”

They don't. Like, that linked document is a cool idea but it's utterly inaccurate as a description of how the tags are used by actually existing website or handled by actually existing user agents (yes, including screenreaders).

Perhaps the tags have not been de facto treated semantically by existing practices. There’s a great deal wrong with the tag soup pervading the web. Current convention doesn’t mean they can’t have semantics.

Potentially they could have semantics in the future, but right now they don't. If you make a user agent that relies on them having those semantics, that user agent will misinterpret a lot of web pages.

I can create CSS to style the two tags accordingly, and in within my own work I can make them mean different things to the tools I use to create and manage html.

Sure. But you could always do that for any tags, regardless of - even in opposition to - their official semantics.

There are only two hard problems in programming: cache invalidation and naming. When programmers give something a name inconsistent with it's behavior, it's going to cause a problem.