Firstly, I agree that Aquaman isn't the shittiest superhero ever. He may not be the most interesting, but he's certainly more capable than people give him credit for. Secondly, the reason this stereotype of "aquaman is shit" is because of that REALLY crappy old Superfriends cartoon, compounded with shows like Family Guy carrying the joke of that show and its iteration of characters even farther.
That being said, I think its funny he has to clarify "I'm not saying he's in the movie." If he's not in the movie, then don't even bother bringing up the subject.