Do you think other kinds of content should be included in the web spec too? So, special tags for musical notation, special tags for all forms of maps and geographic, geological features, tags to represent chemical structures, tags for all major forms of engineering notation, etc?
To me, it's not that I don't think there is a use case for MathML, it's that it's too content-specific to make sense at the browser level.
The only way it makes sense in my head is if I think of math as a language that browsers should support on the basis of internationalization. That makes some sense to me, but if that's the idea then OP is right they should use standard notation (as we do for every other language) and not XML, and it shouldn't be styleable by CSS at all.
To me, it's not that I don't think there is a use case for MathML, it's that it's too content-specific to make sense at the browser level.
The only way it makes sense in my head is if I think of math as a language that browsers should support on the basis of internationalization. That makes some sense to me, but if that's the idea then OP is right they should use standard notation (as we do for every other language) and not XML, and it shouldn't be styleable by CSS at all.