I can think of no better definition of "groupthink" than what you just gave. If you've already decided on the need to self-censor your exposure to "the vast majority of writing on the vast majority of topics", you are lost, sorry.
I have to be misunderstanding you, though, because any time we want to build knowledge and skills for specialists their training doesn’t look anything like what you seem to be suggesting.
> "Groupthink" informed by extremely broad training sets is more conventionally called "consensus", and that's what we want the LLM to reflect.
It's nothing to do with how LLMs work that I wrote what I did, but with this "ought" suggestion of how we should want them to work.