A fascinating thread! I've been following for a long time.
I'm essentially with WCollins. I get virtually all the transits I ask for, sometimes with a slight delay or a rerouting, but usually "as requested".
Often, I've been even more chuffed when the helpful ATC folks have arranged a handover to the next unit along my path - without me asking (or sometimes, even knowing they could do that).
Years ago, I was refused a transit by Essex Radar, and growled (elsewhere) about it. Several ATC folks replied, and suggested I should visit and watch what they do.
Having seen LTCC, Luton, and Swanwick, I have a better understanding of what goes on, and that helps a lot. (Thanks to Warped Factor and Aceatco for that education. Much appreciated.)
I'd suggest that all pilots should visit their local ATC and one of the big centres - it really does help.
I don't argue with the ATC folks about airspace classification - that's down to someone else, and yes I do have some beefs about that! My top bugbear is the Class A down almost to sea level from Southampton to the Channel Islands, which forces me to route across a large chunk of France - under threat from the French military if I get it wrong. I really don't see the justification for that, especially not as Class A.