I am more and more coming to the conclusion that a huge portion of susceptibility to groupthink even seems to be a central requirement to be a "good" trader (as in: one who outperforms the market).

If you just go with the trend most of the time, you take part in a self-amplifying hype cycle that pushes all participants' equities higher. Whereas if you try to "outsmart" the group, you will fail most of the time, even if you might be right in your skepticism, because stock prices aren't strictly based on actual objective reality, but more on the perception of reality by most market participants.