Thanks for the info Bill (again). I know all about rear brake ineffectiveness...try bombing down a fireroad on a mtb and not using your front brake
I will consent that my observations might have been a little "off" during the incident. First the "blam", then the "hmm, tires flat", then the "hey, brake pedal goes to the floor" tends to remove objectivity. I think the train of thought is something like "crap, crap, crap, crap, crap".
It might have been if I'd pumped the pedal I would have gotten something. I've got that ingrained from my days of my '67 bug that had marginal brake systems, but in this case, I didn't really need to panic stop...I could just coast to the right, then ebrake.
The diagonal system at first blush seems to make more sense since you've got some front braking happening, but that might also set the car up for some bizzare handling.