Others could be as productive as me in 8h or 6h or even less for all I know. I just have not met such people. Most people I know sleep little and are by my own standards not productive (I mean I would never hire them, sorry if it is rude)
Your other point also makes a lots of sense: I may be losing 2h per day due to sleep. OTOH, I generally wake up by 11am, am done with breakfast and shower by 1 or 2pm, and start working for real by 4pm, so I'm already wasting time by myself :-)
But in a few hours of highly productive work, I often achieve my goals. When I don't, I very quickly find another way to get the results, because IT NEEDS TO WORK NOW!
Lazyness, impatience and hubris are my best qualities!
Of course, that's not necessarily the case. Everyone has a different genetic need for and predisposition to sleep.