Ok so I quickly scanned the thread and didn't see the answer so I apologize if I am repeating. The thing to realize is that there is a difference between POWER and EFFICIENCY. You can do a lot of things to generate maximum power for short periods of time that aren't very efficient. For general riding, efficiency is more important. For racing, sometimes maximum power is more important.
Exactly. If you want to go as fast as you can for 15 seconds, use all the muscles you have. It's going to produce a lot of power. It's not efficient for any sustained period because producing power by usising your upper body and rocking the bike comes at a high energy cost. Try riding like this for any prolonged period and you'll crap out.
In other words, the best way to produce 1500 watts for 10 seconds, is not necessarily the best way to produce 350 watts for an hour, because the technique that gives you the 1500 watts isn't sustainable for the hour.