I'm not going to counter every point you've argued here on the forums. I'll just address that ones that stood out to me.
David Allen has never said people need to do every facet of GTD to get value. Yes, it is an ecosystem that has many moving parts, but use what you can that is valuable to you. Maybe that would sit easier inside of you, versus trying to dispute the methodology for everyone as flawed because you judge yourself for the parts you don't do or don't like.
As for contexts, here is how David Allen recently replied on that one:
Kelly"Contexts" are only useful to be able to distinguish what you don't need to look at. You can't do errands at home, so it's nice to have a simple "errands" list. If you're in Starbucks and want to do computer stuff, no need to see all the rest. If one simple list works to keep your head clear, though, that's all that matters. - David Allen