sorry,but think about a bike technichians words when he says "the manufacturers ALWAYS make their calculation with the best circumstances possible"
that includes square contact,straight rotor,absolutely no air in the system,no bends in the hose,a defined friction coefficient of the tire,a defined spoke tension etc pp and so on.some even dont make themselves the hassle of testing on a real bicycle,they use a testing machine with a roll thats accelerated to a certain mass and speed and then stopped in different pulses.what you read about the braking power in their catalogue later is just those values
they've got scientists to do that,i think youre going too far again with your opinion being the only truth.comparing laboratory results to real riding is the main problem because everyones setup is slightly different (which starts with the frame being used)
edit:just saying,friction on a brake never is linear or constant,it changes due to surrounding factors changing,like air humidity...
but hey,you wanted to take everything into account haha