"The only issue you're referring is discoverability of extensions from a newbie's standpoint."
shrug I can also say "the only issue you're referring to is discoverability of the advanced features of Word".
"I mean, the very basic task of getting numbered headings in Word is still mind-numbingly arcane for some reason,"
You literally right-click on the "Heading 1" style in a brand new Word document, select "Modify" (as in "modify this style", quite obvious), under "Format" click on "Numbering" and select one of several numbering styles. I spend more time looking up how to do Markdown numbered headings markup than that - and that's not a complaint, I don't spend a lot of time on that at all.
Look, I dislike non-semantic markup too. But all the whining about how if only those Word using idiots would just switch to Latex and all would be well in the world is getting old, and not only that, it's just wrong. Yes it's easy to make a pdf that looks like the default ugly Latex style, but beyond that, it's a massive time sink for even the tiniest modifications. All of these tools suck, some just suck a bit less for specific jobs than others. Claiming that Latex is 'superior' to Word is like saying that a tractor is superior to a bicycle because you can't pull a plow with a bicycle. I mean, sure, that's true - but there are many more criteria for judging modes of transport, just as there are multiple for document preparation systems, and Word wins on some criteria and Latex on others.