I think I take a couple of issues with the OP, if I understand the OP's argument (which admittedly I may not). The first is it kind of creates a false dichotomy between games that are non-GM driven* as non-railroads and all other games being railroads. There is a big difference between a traditional* game that is on a set of tracks the players can't escape from and traditional game where there is a vague outline of a track but the players can go in any direction they want if they choose, versus a game where there is no track and the GM uses restraint in order to maximize a sense of fairness. So I think there is a bit of a false division here
On authenticity I think it is a very loaded word, but taking it in the existential sense and in the sense of being true to yourself, the argument of the premise could also be used to make the case that the most authentic people are those who have the most power and money (which I find deeply unsatisfying). I realize Pemerton didn't make this argument in particular, but by equating the amount of power players have in the game*** itself with their ability to be their authentic selves, I think that misses the fact that authenticity can very much exist within constraints (i.e. the GM being able to fiat an Owl Bear encounter doesn't nullify my authenticity, my authenticity is in my reaction to that owl bear encounter).
I may be missing something here or projecting assumptions about systems so perhaps I am wrong.
*Unless by GM driven he just means railroads but I got the sense he was talking about games that empower players mechanically
**Not hung up on this word, just trying to make the point
***Again if I am correctly following his argument which I might not be