Well yeah it's simplistic, since it's 2 sentences. I'm not really prepared or qualified to write a 30 page paper on the nature of medieval combat. Yet there seems to be an obvious truth to it.
There are of course exceptions, such as persuading or paying someone else to fight for you, or concealing a weapon, getting someone to trust you, and stabbing them in the back, etc. It still seems to shape much about reality to know that the majority of people will have no chance of ever winning a remotely fair fight against the enforcers of whoever is in charge.
I don't find the "truth" you mention obvious at all. I think it's just a fairy story simplification based largely on fiction (written and visual).
Over the last couple of thousand years (or more, but history gets a bit fuzzy beyond that), lots of nations have had leaders at many different times who were not the best fighters.
Your claim wasn't that a majority of people had no chance of winning a fair fight against enforcers, which is obviously true. You made a much more broad claim about how historically certain physical attributes would put particular kinds of people in positions of power, and about how that has changed.
I think this is likely misleading and inaccurate. Yes, those with power have always used force to enforce their wishes, but that's very different from saying that those in power are themselves of a certain physical type.
There are of course exceptions, such as persuading or paying someone else to fight for you, or concealing a weapon, getting someone to trust you, and stabbing them in the back, etc. It still seems to shape much about reality to know that the majority of people will have no chance of ever winning a remotely fair fight against the enforcers of whoever is in charge.