I don't think their assertion is that someone with 40+ years of math experience would have difficulty learning new notation, it's that LaTeX is composed of a lo

I don't think their assertion is that someone with 40+ years of math experience would have difficulty learning new notation, it's that LaTeX is composed of a lot more than straightfoward notation. LaTeX can get pretty complicated pretty quickly. While it's basic math notation is quite fantastic, it's the basic document formatting that I think would give most people trouble when learning.