For one, if you try to throw your arm around somebody and somehow manage to hit them in the face that's still a valid case for a red card!
You can even see his fist is clenched. If he was trying to grab him the hand would be open. There's also the fact that you don't swing the arm horizontally at face height to grab somebody - it's either horizontally at torso height, or coming down over the shoulder. There's no way on earth that this wasn't a punch - and it's a positive thing for the game that we're now setting the bar quite low on when a punch warrants a red card. Anybody who thinks 'yeah, it's a punch, but not much of one, it's all good' should be watching a different sport (not you, you just don't think it was at all. Which I find more confusing
)
As for obstruction from Bujis - my view on that is that Roy wasn't actually obstructed. Bujis meant to, yes - but Roy got in first and punched him before his run was actually affected. And attempted or intended obstruction isn't a foul.
Worst case, both happened at the same time - in which case it's still a red card and a FK to SFC (more serious foul). That could well justify a card for Bujis - but a card's justified by his disgraceful acting anyway. Although that could provide a good excuse for the ref to card him...
As for your point about the VAR, that doesn't make sense to me. We only use something like 4 cameras at a game, and none of them are even high speed cameras. That can create problems with viewing things - as we can see here when the arm is a bit blurry due to the technical limitations of our cameras.
I think you're misinterpreting the idea of 'clear and obvious error'
IMO it doesn't mean it's an error that's easy to spot on video – but that once you've seen it on video replay, you couldn't really make a reasonable argument in favour of the ref's original decision.
Look at offside as an example of the misunderstanding. We've seen VAR overrule offside when there's been a matter of inches in it....but in those instances it's quite clear what the right decision is, and people are saying 'but it's not obvious if it's that tight'. Or trying to argue that 'obvious' means you expect the AR to have gotten it right in the first instance, when if it's that tight you wouldn't expect that, which I think is a complete misunderstanding.
Perhaps it needs to stick with 'clear error'.
Also, your approach could be inviting wrong decisions as well - sometimes something looks like a foul at full speed, but when you slow it right down you see that the studs weren't near the leg, or the ball hit the chest and not the arm, or that sort of thing. Watching it multiple times at different speeds can sometimes exonerate a player, especially as things can look completely different at different angles.