Part of the reason we use that 100 hour figure is for someone's first game, when they are still learning the engine. At that level, it does usually take about 100 - 300 hours to make 1 hour of good content, just because of all of the doing over you will be doing. But...once you get more skilled, then you can probably go faster. I still remember that 40 hour spurt where I churned out 2 whole hours of content, as I knew exactly what I wanted to do, and how I wanted to do it. So exceptions can exist.