"I wouldn't go so far as to dictate that to you." That aspect is best left entirely to Watson's discretion because that's the part that's infinitely fascinating. "But am I not allowed to make suggestions to the current situation as the story goes along?"

The ideas Watson presents sound good to him; truly he doesn't know that he would complain about the plot itself, unless it was unrealistic or problematic or ridiculous... But he can suspend some of that for a story, at least.