For info, as an update on point 4 HIGH IMPACT - Hold points for 27R I have been carrying out some tests on the A1- A3 taxiways for feed into the start of 27R in the last couple of days, with some input from another couple of well known forum contributors, and will not proposing any changes to this as it works pretty well with respect to the known game issues on aircraft proximity warnings, aircraft sizes etc. You can "stack" aircraft here fairly accurately with careful planning and controlling.
The hold points are roughly where they should be and the only real issue was that I think that the A3 Hold Point should actually go back slightly
I have now completed a few tests on Runway 27R departures
Once I was aware of the restrictions it seems to work as expected
The issue you found with the A3 holding point is due to a controller experience issue
It is highly unlikely a B747 would be sent to A3 via taxiway A, the preferred route is taxiway B
This then keeps A4 free for aircraft arriving along taxiway A
Equally, it would be rare to have more than three aircraft holding at each of A1, A2, and A3, as this would back up beyond TITAN and SATUN