Often looks from an end users point of view that Glasgow can pack them in that bit tighter
This may be too simplistic a view.
Two points to note
EDI is about 15% busier than GLA (movement wise) and is working at capacity and therefore slot constrained at peak periods.
Queues increase exponentially the nearer you get to capacity.
Having made these two points, how does this affect EDI.
A useful analogy is the wondrous traffic jams you encounter each and every day. During the school holidays they are small, but when the schools go back and the traffic increases, typically by about 7 to 8%, the queues are often 10 times as long.
Once a queue starts, normally a 1 to 2% increase in volumes will produce a 100% increase in the queue length.
Also, the busier you are the more likely multiple arrivals will appear at the same time and this causes more queues (extended routing and all that). Unfortunately, during busy times, once the queue develops there is not the slack to clear it (as the operation is working to capacity) and, as a byproduct, everything also becomes more inefficient as time is taken managing the queue.
So the perception may be that GLA can pack them in better, the truth is that the volumes are lower making the management of the arrival traffic easier. That does not mean that GLA ATC may not also be better, but may explain why EDI is perceived as worse (which may or may not be the case).
In this sort of environment, it is extremely difficult to operate much is excess of 90% capacity without a queue building up and the closer you get to capacity the quicker the queue will grow. So a busy ATC operation has my deepest respect wherever you are.
Ex (Not a pilot but a statistician to trade)