Half the things you've described aren't even placebo.
Ex: If you use no viewmodels for 3k hours and suddently turn viewmodels on you're gonna have a hard time aiming because you are used to aim with the crosshair not with the viewmodel + crosshair, it's not placebo, your hand eyes coordination will suffer because your eyes will have trouble focusing as effectively as they did to the crosshair only
Claw grip interacts with your muscles differently than palm grip so your aim / reaction times might feel different because its all about muscle memory.
etc, etc..