Latex is not semantic, the fact it's using macro (which are factoring function calls) says it all. There is some degree of separation between content and presentation, but that's it.
LaTeX as designed is generally semantic (formatting is left to the applied style), and whilst HTML5 is in theory reasonably semantic, in practice, LaTeX tends to be used far more semantically than HTML is.
Some of those reasons are technical, though as noted elsewhere in this subthread, economic and other factors seem more dominant, and I severely doubt that LaTeX on its own will address the broader scope of issues raised in TFA.
To respond to your question: no. Not sure why you linked me the PDF 2 specification. PDF/UA is from 2012, and the ability to tag PDF files for accessibility is a thing since 2001 (with PDF 1.4).
Various tools and packages that attempted to generate accessible pdfs from LaTeX have existed for aeons, all of they had a common characteristic: they sucked. I am convinced that by this point everyone who cares about accessibility has moved to other formats (like HTML).
TeX itself is a set of typesetting primitives. LaTeX is a set of structurally-semantic, document-oriented macros built on TeX.