I could sort out VAR in an instant.
Offsides - All reviewed by technology. Linespersons call based on an agreed margin of error either way. That eradicates those calls that are ruled offside by a little toe.
Penalties and Red Card offences. Each team have 2 refer to VAR's called only by either the captain or manager, like with cricket only a short amount of time post incident to make a VAR referral otherwise it is tough. VAR officials have, let's say up to 5 views of incident, all in real time, no super slow mo and only if there is a clear and obvious error is it overturned. Then the VAR announce the decision, none of this stupid going back to the monitor rubbish and letting the ref have a look.
Any decision about whether balls have cross the line - We have goal line tech for that which seems to work well.
Then if a decision is ruled in the favour of the team making the VAR call they retain their review, if not then they lose it.
In my mind that would make the Southampton non-penalty we had a clear review by Rooney and a clear overturn. It probably means that the WBA decision is kept as a penalty because after 5 real time views it isn't a clear and obvious mistake on field by the ref. Simple!