So, taking the latter one - what happens when the ref *doesn't see* what happens, like even slightly. Take the Man City Chelsea penalty controversy - where Grealish clearly moves his hand to block the ball in the wall. The ref *clearly* didn't see what happened (as he gave it as a goal kick, so he didn't see any contact) - why wouldn't you want VAR, in that situation, to exist - and to then tell the ref "look mate, you clearly didn't see Grealish handle the ball - can you go over to the screen to watch the replay so you can make a better decision on whether you think it was ball to hand, or hand to ball".
I can understand VAR being reluctant to give refs instructions - the on-field ref is in charge of running the game and they can't be seen to undermine him.
But refs need to be more prepared to admit that they are human, liable to make mistakes, and proactively ask VAR for guidance and support more often. Not instantly assume they are correct even when they have a limited view of an incident.
Basically, it needs to work more like TMO in rugby, which has proved hugely beneficial to the game. It's mad that they can't even establish a consistent process in football. If there were some consistency, the occasional mistakes would be more forgivable.
Instead, the "mistakes" often end up looking like something more sinister, especially when they appear to consistently work in favour of certain teams.