Again, you can't make as many Joker solo films as Batmans because he's a bad guy, you can't do a procedural structure here, but the character is definitely more popular than Batman. Suicide Squad box office was carried by him, a much better sequel dropped like a rock as soon as he left. The Dark Knight had this massive increase over Begins precisely because of Joker. Tim Burton's Batman did what it did because of Joker. The Batman didn't even cross 800 mln despite glowing reviews, he gave nothing to Justice League and it flopped. Numbers are numbers, can't argue with them.