Your last paragraph.....this is why sometimes I wonder how/if those aftermarket water pumps are always able to back up their claims. I understand the pumps with more or bigger blades on them can move more coolant, but can it not also move more coolant through and out of the radiator before the radiator has the chance to do it's thing? Along the same lines, the coolant lines from my and most bikes goes from the head/cylinder to the top of one radiator where there is a crossover tube to the other radiator and then the bottom of both radiators plumb back to the pump. It would probably be a hassle due to the extra plumbing, but seems like it would be more efficient if it went from the head/cylinder to the top of one radiator with no crossover tube then to the bottom of that radiator, then to the top of the other radiator and then out the bottom of that one to the pump. Maybe it wouldn't make enough difference.
The thing to remember is that the coolant in the system also works via convection. That is, the faster it flows over a hot surface, the better it draws heat from it, and the faster it flows through the radiator, the faster it hands off heat to that surface, provided it is cooler than the coolant. So as long as you have good convective cooling of the outside of the radiator, the faster you circulate it, the better it works, within limits.
I doubt you'd see any improvement by way of the alternate plumbing routing you suggest. Water files into the radiator top tank on the left, where it encounters enough resistance to encourage it to flow across to the opposite side, then down through both sides tithe bottom tanks, then out. Not much advantage in splitting the outlets the tanks just to converge them again at slower point.