A couple thoughts:
The first is my perspective as a new diver in this configuration. I'd agree it isn't the "best" per se, but that it is very adaptable and doesn't have to be tweaked as diving evolves. One example for me was my first scooter experience. I had never really thought about the front crotch-strap D ring, and had no occasion to use it. When I tried out an X the other weekend, it was as simple as getting in the water and clipping the scooter off (at least from a gear perspective-managing the scooter and the task loading was something else).
My second point is that, the finer points of the gear configuration start to become handy. I've adopted the extra double-ender on the right D-ring approach, and I find I use that not only to clip off my light but, for instance, to clip off the X on my left d-ring when I was leaving the water. It is clear to me that people with massive amount of experience (beyond where I will go with my diving) have thought this configuration out, and because of that, I am fairly confident I won't have to reinvent the wheel as my diving evolves.
That being said, I agree with the doubles/singles rigs being separate. I found that my DSS plate works better as a single rig, and a FredT plate worked better for doubles, because the deeper bend in the plate was more comfortable. I'm also contemplating a Kydex plate for a travel rig for the weight savings . . . so at the end of the day, I'd agree that the one-size-fits all plate thing is a possibility, but probably not the optimal solution if you are diving varied rigs. But, at least plates are relatively cheap.
