How effective can critical discussion be as the primary mode of learning more in a field once you reach the very top of the field? Once you know all the common ideas and arguments, then people who only know those common ideas and arguments can be of little use.
Or perhaps not. If you have a new idea, then the reactions of those same people to the new idea will be new to you.
But what if you are so far ahead of others in the field that their reactions to new ideas consistently contain nothing you didn't already consider? Then critical discussion wouldn't be especially useful. Is such a scenario realistic? If one was in it, should they make progress by critical discussion within their own mind? Or should they find another field to work on? Or should they teach others and help them catch up? Or should they make progress in this field by some other method?