Despite an effort by CDPR to detail in the description of the Sandevistan Operating Systems that they do not slow you down, they still do slow down V.
Sandevistan is supposed to be super speed ; time isn't actually slowed down, it's just that V becomes insanely fast, but for gameplay purposes, it translates to everything around you being slowed down.
Since every Berserk OS is now tied to Melee weapons only, I wanted to give a try to Sandevistan to help my Shotgun build since they aren't usable with Berserk anymore.
However after some testing I can 100% confirm that V is still slowed down herself when using Firearms while using Sandevistan. Shooting and reloading with any ranged weapon is slower, making them feel so much worse while Sandevistan is active. For some reason this is only the case with ranged weapons ; melee weapons keep their normal attacking speed.
Either this is a bug, or it's something CDPR failed to detail in the Sandevistan descriptions. I doubt this is a bug or intentional though because either way, it doesn't make sense.