Well, my thread about "Why do we teach flutter kick?" had to do with the fact that a frog kick in reasonable trim is a useful kick in the vast majority of settings, whereas the full-leg flutter kick is an awful kick in a lot of settings, especially the ones I read about people getting certified in, like silty lakes and quarries (and of course Puget Sound).
I do think, after seven years of doing this and helping to teach, that "donate the primary" is a better strategy than fumbling for an octo, and the bungied backup (or even Air2) makes better sense than trying to secure a secondary regulator somewhere where it's visible and easily released, but doesn't come loose on its own.
There are a lot of things from the DIR system that I think would be really beneficial to the big mainstream of recreational divers. Emphasis on good buoyancy and trim, non-silting propulsion (and a spectrum of kicks for various purposes) and maneuverability in the water, practice and facility with emergency procedures, good dive planning and gas planning, and strong situational awareness are ALL widely applicable in diving. As I said, I like the "donate the primary" approach to gas-sharing as well. I like the emphasis on positioning for buddies and maintaining communication -- if you ARE going to dive with someone else, it makes no sense to pay no attention to them!
There are a lot of ways of diving. Some of them are controversial, and I think, no matter how positive you are about solo diving, you'd have to admit that it still falls outside the way diving is taught at the basic level by all agencies. Diving vintage makes buddy diving a little complicated, if you accept that one of the reasons for having a buddy is to donate gas in the event of a loss; I know you CAN buddy breathe with a double-hose regulator, but wouldn't you agree that simply donating a secondary reg is a whole lot easier, and less stress on the OOA diver?
We could go on . . . GUE has set up their equipment and procedures because everything makes sense to them, and those of us who find it makes sense for US, too, follow the guidelines. For those who don't find the arguments compelling, there are lots of other ways to dive. Every single equipment choice or setup, or choice of procedure or protocol can be argued, and what you decide to do depends on how much weight you give to various positive and negative aspects. We will never, not until the end of ScubaBoard, bring everyone here into consonance on how diving should be done, and I don't think it's worth trying