Matan1, where do you see that in the Rambam?
Also, it’s been a lot longer than a couple of hundred years that poskim either argue with the Rambam or say that he would agree in a different era. See Kesef Mishnah on the Rambam.
It is beyond me how people use the Rambam against kollel when that Rambam is clearly not halachah l’maaseh.