Imo VAR should only exist in a technical capacity to prepare footage to transfer onto a ref’s portable Fold 5 or something. Samsung could sponsor it even!
The decisions should all be made by the ref on pitch and this would massively improve the speed of play during VAR. There’s no reason they should have to walk off pitch.
The monitor is bigger so you can see more clearly, the phone can get damaged during play, it’s easy to keep players away from the monitor because they aren’t allowed to leave the field, etc.