For me there are simple ways to solve this
1. Any player goes down injured( non-head injury), play continues and the trainer is waved onto the pitch to deal with. The player then has to leave the pitch for the same amount of time he has been 'injured' .
2. Head injuries. If player claims a head injury, he is escorted from the field and assessed by an independent doctor. To ensure there are no delayed effects, the player has to stay off the pitch for 5 minutes after which time an independent doctor assesses the player to confirm they can return to the pitch amount. This is for player safety
3. If the player has been clearly concussed at the outset on the pitch , a concussion substitute is used anyway
Im not sure it is that simple. I think most fans would agree with anything that would reduce the amount of cheating / shithousing / 'game-management' that sometimes ruins things. However, your solutions would also punish the 'victims' of genuine fouls or injuries including, for example:
1 McAtee Bristol City v SUFC
2 Baker SUFC v Bristol City
https://www.bristolpost.co.uk/sport/football/nathan-baker-hospitalised-sheffield-united-6273685
Now, if we could find a way of sorting who was genuinely hurt it would make things simple, but fortunately (or unfortunately depending on your opinion) protecting players is the priority. We all want to stop players 'taking the piss' but again it is often hard to 'know' so refs have to be cautious (and most fans I sit around are totally biased so we can't claim we know better).
On VAR I'm a bit more supportive than most, although I totally agree with the argument it can impact on the spontaneity of enjoying the game... and I don't think that is worth sacrificing for a small % of more accurate decisions.
However, what I think is positive about VAR is the deterrent. IIRC before it came in there was so much 'gamesmanship' going on that the officials couldn't be expected to see, but if you know VAR will check when e.g. you 'cheat' in the box waiting for a corner (I remember thinking VAR reduced the ridiculous amount of grabbing in the box so Harry could bang in headers at the 2018 World Cup). I also think the amount of screaming, rolling or holding your head (for nowt) while looking for a red has reduced. IF this is the case, then maybe VAR is a price worth paying?
Although I do like the idea of more retrospective punishment suggested by
bertieblade ... it also opens a massive can of worms. Can you imagine missing promotion determined by a decision that was retrospectively changed... lawyers could be all over it!
I wish the game was more simple... and (if needed) that we can another offside goal to get us to the top of the league tonight!