In some sense the startup is lower cognitive load, because everything is great until it all implodes and then you look for a new startup. A punctuated equilibrium. At a megacorp, everything is vaguely doomed all the time, but never so clearly doomed that it's obvious when to make a move, and you spend a lot of time reading political tea leaves so as not to end up on the wrong project.

The worst thing that most big companies do is continue to employ good people on long death marches.