Like so many tools that originate in that time, it is very efficient after an initial learning curve. I use LaTeX to typeset theoretical CS things (papers, exercise sheets, ...), and those often contain a fair amount of mathematical notation. Expressing them in LaTeX math notation comes quite naturally to me now and doesn't require much thought at all. And when I do miss some symbol, there are excellent tools like http://detexify.kirelabs.org/classify.html.

I’m curious - what’s your definition of efficiency here? I would include learning time in that, plus cognitive load, and it’s clear you are not.