If you have a look at all 3 terminals, you can see that when they were built with 2 drop off/pick up channels outside the terminal, however due to the incident in Glasgow, it now means you can’t use the one closest to the terminal which puts more pressure on the remaining channel.
It’s due to this that traffic builds up, so I’m not blaming MAG, because it’s outside factors that have meant this.
If somebody driving a car with explosives into a terminal building is the issue, then simply erect bollards along the length of the building. The closure of the forecourts at UK airports is an over reaction to an event that happened many years ago.