That 1 gram a watt yes is possible but let's be honest here, the average grower is probably closer to bags guesstimate for dozens of different reasons. I'm not expecting to duplicate the hps results but if it can get ballpark even if its watt for watt the heat aspect tips the scale, for my situation anyways....
I can't say what the "average" grower will yield but that doesn't change the fact that HID can and does exceed the 1g/w mark, despite claims that it cant, and LED hasn't hit that mark yet. Regardless, if an "average grower" is getting much less than possible with HID they'll get much less than possible with LED too. Experience will certainly help but the myth that smaller LED lights can replace much larger HID lights is still a myth...based on results.
Disclaimer: I still use HID and I'm NOT an LED expert. All of my LED knowledge is from other parties or research so I can't say from first hand experience one way or another. I also run a medical grow consulting business in SoCal.