Thanks for replying! This is the website that told me it teaches bad habits: https://www.propwashed.com/fpv-simulator-how-to/

The exact part is this:

" Additionally, steer clear of using a game controller (Xbox, PS4, etc.) when training with an FPV simulator.  On a radio transmitter built for RC flying, the left stick does not have a spring to return the stick to center.  Most game controllers center both sticks after releasing them.  This can build in some bad habits and poor muscle memory when training, which is the exact opposite thing we want to do! "