Amen, I think if memory serves correctly HTML was SGML inspired and once XML became popular there was a XHTML standardization push for a brief time.
I think you could argue that the ubiquity of HTML led to people see value in something like XML back in the late 90's / early 00' and HTML drove XML invention and adoption and not the other way around.
And HTML + CSS3 is Turing complete without Javascript anyway: https://accodeing.com/blog/2015/css3-proven-to-be-turing-com...