'the best ever at fighting'

he gets crippled by a mage with a stick. he gets killed by a peasant with a pitchfork. he is repeatedly put on the back foot by regular ass dudes.

every person in the setting that isn't also a witcher or a mage rightfully sees him as an inhuman monster

he's literally just a human, the myth that witchers are some kind of monster comes from the fact that many of them turned to banditry in order to survive because they had already hunted all the monsters (there are a finite number of monsters in the world since they are extradimensional beings that don't breed). geralt is constantly starving because he doesn't have any money because he's above banditry.