Fakemaly but SDL can't handle some fast mouse flicks in newer kernels properly, so raw input screws it up).I read somewhere (I think in the mastercomfig discord) that deleting the SDL. so file in the TF2 folders fixes the double mouse input problem with raw input. Seemed to work for me.
This is because by deleting SDL.so file you make TF2 load system version of SDL rather than the one that is shipped with Steam itself. SDL fixed the double sensitivity issue long ago, but Steam version is still not bumped.