I think Manouche is pretty accurate with his theory, and 55 minutes would be the sweet spot purely for GS purposes. What he says is that most people on the forums also take into account the desired performance, increasing the ideal minutes to a higher amount of 60-65 because you want to play your best players as much as possible. So if you take GS and game performance (output) into account, the sweet spot is higher.
I like Manouche's view on equilibrium, temperance and compromise. There is no one way to optimally manage your team, there's always pro's and con's and that is what makes the game fun. I can imagine this is easier to accept for people who for example study business administration as opposed to a technical study, because most business problems are about equilibrium, temperance and compromise while techinical problems are usually about finding the one or at least limited optima.