Even if flow control tells you to expect considerable holding, if an aircraft can't land because you are occupying the tarmac, another problem arises.
Using Miles as the particular example, most pilots I would expect plan to arrive overhead with some reasonable amount of holding fuel and enough to go on to Roma or back to Chinchilla. Of course, at the fuel planning stage we have no idea how many aircraft are queued up ahead of us, or what their COBTs are, so what we add for contingency fuel is a guess at best. And all constrained by landing weight, given that it is such a short flight from BNE.
So, when that reasonable amount of holding fuel has been used, unless the aircraft on the ramp is about to launch and this is verified by both crews talking to each other, old mate still in the air either diverts, or accepts the risk of becoming a glider. And then there is still the risk that the one on the ground goes u/s after starting. This already happened. When aircraft are forced to divert, it creates a right clusterfckuk for the workers scheduled in and out on that shift.
Commercial pressure is now in the mix. Not good. Someone, please just fix the f....ing parking and taxiways! Or the airport operator could engage someone who understands the problems to control slots into Miles.
Meantime, of course we are still expected to call flow control before starting engines as per NOTAM etc, but often it seems that a deliberate decision to go 'non compliant' is actually for the common good in the grand scheme of things.