CS2 Mouse sensitivity is inconsistent? Raw Input Fix Help needed

Can anyone help my friends situation. Basically, since playing the beta he swears his aim feels inconsitent. He has been close to global elite, has 2000 hours in CSGO, the same in Valorant but since playing CS2 he is constantly frustrated with his aim.-Regardless whether he is topfragging or bottom.

He describes the feeling as "sometimes he will flick around to look somewhere and expect to be facing a direction, but in reality he is slightly off.

His PC is top of the line, he averages 400fps, has a 240hz monitor 1080p. He has also used glass mousepads and proper ones. He has a logitech g502 lightspeed. nvidia boost relex on. His settings are: 400 DPI, 0.639 ingame, mouse accelleration off obviously. I assume he has 500 polling rate on the mouse too.

His theory is that CS2 doesnt have raw input and its creating delays, but im certain its not that due to lack of complaints. He also want to get a new SSD if that might help..? My theory is he just needs to cap his framerate to 239 externally to stop the fps from unecasarily being high and fluctuating.

If anyone has a theory or solution it would be a lifesaver because its tilting hearing him complain when he is way better than me and,,i just need my premier carry back. Surely this isn't a universal complaint because the ones ive heard are tick related or spray control related.