Honestly, I think that academic disciplines, or even schools, where everyone is completely full of it are extremely rare.

That isn't the point. Sincere and intelligent people have been coming up with novel ideas on important topics long before scientific methodology was even a sparkle in Galileo's eye.

Most of those ideas were worthless. Most modern ideas are worthless, too. The question is: how good were they at distinguishing the worthy ideas from the worthless ones? The sheer number of recently-discarded fields, much less ideas, should make it clear how well the ancients discerned the gold from the dross.

What's the signal-to-noise ratio? How much care is taken to ensure that people aren't deluding themselves?