My lack of knowledge! It's a frigging rear seat, it is supposed to be intuitive! Why does my sienna have 2 (count them!) belts to pull - one to fold the back, the other to drop the seat in the cavern, and YOUR GC has FOUR!. It's a friggin algorithm there, and if you do not follow it, the seat does not fold, and you start over..... I should not need to read a manual to fold a seat. Heck, I DIDN'T for the sienna, nor for a sedona I had as a rental last year.....
As for tumble - perhaps you are right, except to get an adult into the 3rd row, moving the seat does not seem to be enough. We needed to tumble them. And just because we did, this still does not explain why the headrest chooses to fold every time.
As for stow and go, it is a compromise. Yes, you do not have to take the seats out, but the seats are quite thinly padded, and the butt angle is wrong. Also, you cannot put proper carpeting in there (e.g. Weathertech) with all the foldy carpeting bits. Yes, the folding mechanism is quite well designed, but I am not sure how long it will be before it seizes due to all the sand / salt / muck that invariably gets in there.
And I notice there is no contra-argument to the fact that it is still narrow in the rear.
What I stated was were _observations_, based on my own experience of putting one of these through its paces on hwy, sand, in pouring rain and with 7 people on board for 2 weeks.