Over flat ground there is only a very small penalty for being heavier, but there is a huge potential to make more power being a larger person.

Let's say we have two riders who both an FTP of 4 Watts/Kg. One of the riders is 55 Kg and has an FTP of 220W. The other rider is 110 Kg and has a FTP of 440W. Looking strictly at their watt/Kg you would say they were equal. But when I run the numbers through a calculator the larger rider will clearly be much faster over flat ground and effectively equal to the lighter rider up hills.

Over flat ground the smaller rider could only average 20.6 mph. The larger rider could average 25.7 mph. Up a 5% grade the smaller rider would average 11.4 mph and the larger rider 12.9 mph.

Granted these are theoretical numbers from a calculator, but they mimic my experience as well. I've ridden with bigger riders who have similar output in watts/kg but who are much faster because there is basically very little penalty for being larger over flat ground.

So am I just missing something or comparing riders based on their Watts/Kg completely useless without taking their total power output into consideration?