The problem is that setting the font to sans-serif, will not set the math-font to sans-serif. See https://stackoverflow.com/questions/2537868/sans-serif-math-with-latex-in-matplotlib for solutions.

As ScalarFormatter always uses an equation when formatting when usetex is used, the math font will be used. You can try this out by e.g. formatter(2) in your example.

To get around this, you can use the FormatStrFormatter just as you have done (but set it for the major ticks and do not call set_xticklabels).

I appreciate you looking into this. I understand math text needs to be set separately, the problem I've been having is mathtext.fontset doesn't work at all so I was trying to figure out a way to turn the math text into a string in order to keep any previously set formatter (which both my and your solution's don't do since formatstrformatter can remove exponents/symbols from the previously set formatter).
I can open an issue for math text not setting instead, but I also wanted to see if this way is possible because it's simpler for my code than adding if statements for each possible user input for the font. Please let me know your thoughts, thanks!

the mathtext.fontset rc param controls the behavior of the built-in (to matplotlib) mathtext (usetex=False) implementation of a subset of LaTeX math mode, not the font when using the full usetex=True LaTeX.

Ref: https://matplotlib.org/stable/users/prev_whats_new/dflt_style_changes.html#math-text

If your usage is supported by mathtext (without calling out to full LaTeX), then that may solve your immediate issue. otherwise it will likely mean some combination of tex.preamble and wrapping your fragments with e.g. \mathsf{...}.

I see, that makes sense. Thank you both for your help, I really appreciate it. Taking mathtext and turning it into a string so the font applies is probably not possible with exponents/symbols as well.

I'm guessing this is more of a feature request to allow mathtext font changes when latex is set to True then, should I close this and make that request?