I think what he meant was more like losing weight would make it easier and less taxing to produce 200 watts. Like at 220 lbs it might take 250 kCal to make 200w but at 200 lbs it would only take 230 kCal to make 200w. Maybe that's not what he meant, but that's how I took it because how else would you measure the efficiency of producing 200w? (If it's going to improve with weight loss, that improvement has to mean something, it has to at least theoretically be measurable.)