Very interesting Mr Surreyman.
I was just thinking about Amsterdam, where there is barely a single seat in the departure pen and you can be trapped in there for ever.
Above is a reference to Manchester. easyJet only transferred to Terminal One quite recently, and it is indeed appalling to be sent down down those 1960's stairs from that inadequate pen into the freezing pit to await the eventual release into a Manchester downpour.
In UK I don't believe it is down to the airport at all. Airlines these days have a lot of clout with airports. And even if the physical facilities are tight or prehistoric, the airline can easily add a human touch to make it bearable.
An example is Jet2's check-in area at Manchester. Arrive at the door and your heart will sink as you view the usual 0600 heaving mass of humanity... until you find yourself welcomed by one of an army of red-fleeced assistants who will smooth your path. Suddenly you realise that the whole thing is under control and it doesn't seem so bad.
In summary, I'd say that easyJet has complete power to move passengers around just as they would like to. Either they are choosing to do it as they are now, which is appalling, or it has evolved like this because nobody has really given it a thought.