Interesting. What browser? Because in FF or Chrome on Linux desktop, it looks basically identical to LaTeX output. But unlike when creating PDFs, you’re at the mercy of your browser’s MathML implementation (another reason PDF is great).
EDIT: I just checked the article on my phone, and every browser renders the equation as in your screenshot. FF and Chromium on desktop are perfect. Another example of how mobile browsers suck.
So authors using MathML should supply the LM font for download or advise their readers.