Yeah, field size should not be underestimated as a factor. However, neither should confirmation bias. The big name pros like Daniel aren't always at the final table…you just only hear about it when they are. 🙂

In terms of an actual answer to the question, yeah, less mistakes is going to be pretty much the biggest determinant of edge at the highest levels. Another contributing factor is having experience in every aspect of tournaments – most of the guys who crush MTTs the hardest either have excellent postflop skills after moving over from cash games, or are great at playing with a sub-40bb stack as a result of thousands of hyper-turbo SNGs. HUSNGs are also a breeding ground for some of the best tournament players, since they require so many of the core skills necessary to become good at tournaments.

By playing tournaments alone, you really don't get the experience needed to become good at every aspect of the game unless you either grind very high volume of MTTs online and live, or you spend time in other games to develop your skills in areas you're only rarely exposed to in MTTs, such as playing with >100bb stacks, or playing short-handed.