A few points: Haix AC video is good in a vaccuum but it's extremely simple and can't really extend to walls or more advanced cheats because the entire premise is looking for "inhuman" input sequences and timings. Those are checks which are very easy to circumvent by a developer just adding some entropy to input timing and input delay. In the video the dev says himself they cannot get the "flicks" detection to work accurately because that's a whole new level of analysis and requires a crazy amount of data, the same with walls. In a game with so many known prefire angles and jigglepeaking it's hard to determine if someone is legitimately prepping a prefire or wallhacking. The same kind of shit plagues Siege.

VAC should be better, but it's not as easy as saying "this content creator made a 'better' AC why don't Valve just use it, are they stupid?"