That's exactly why VAC works the way it works. Other ACs, like BattlEye or Faceit AC, will conflict with other 3rd party softwares and hand out false punishments. I'm not saying VAC deliberately ignores cheats, I'm saying that it does not automatically ban you for using certain 3rd party software. Again, yes BattlEye and Faceit will ban more cheaters, but they will not have a 99.99% accuracy in their bans, which VAC has.
VAC is fair. Like I said, almost 100% of all VAC bans handed out are deserved. There are no unfair bans.
The firm has actually invested A LOT into anticheat measures, it's just not that known in the public eye. VACnet is a deep-learning AI that learns from Overwatch cases to detect and automatically ban blatant cheaters faster. If someone is spinbotting, chances are VACnet will ban them faster than the Overwatch system could. Not to mention Prime, Trust Factor, Overwatch, and now Trusted Mode, all of them measures against cheating put in place by Valve to increase it's effectiveness. I can agree that, yes, they could have made a much more effective AC system, but it would not be as accurate. And to say they haven't invested is plainly wrong, though their investments might not have been as successful as you wanted them to.
Nearly all of Valve's game improvements are based off community feedback. The only two things I can recall that the public often speaks about that hasn't been implemented is Source 2 and 128 tick MM. Valve have said a Source 2 port would be an extreme hassle for very little improvement, so it is unnecessary. About 128 tick I'm not sure, but the statistical data suggests there is not much of a noticeable difference between the two.
About skins, Valve needs to strike a balance between catering to the competetive side of the game and the casual players. There are a lot more casual players than competetive ones. The reality of CS:GO is that most peiple care a lot about skins. They need to add skins to keep the game afloat and keep the player numbers up.
As for the player skins, I think they've done a good job of patching them. Not much else to it, I think if they introduce even more ones it could be a well implemented feature and a good way to customize your experience even more.