Originally Posted by Binker
There are reasons for that, as many have explained, plus some more too. Like others have pointed out; Superman at that time didn't know any of Batman's villains, and never thought how crazy or powerful in their own right they would be when he confronted them. When Joker threw marbles at them, no one would think they were grenades, not even in the real world I might add. But as Batman said, "expect the unexpected" when it came to the Joker. In Knight Time: the villains were easier because it was Mad Matter and Riddler (also Roxy from the opening), even Bane was easy for Superman because he was pretending to be Batman and playing weak. In Demon Reborn, Superman was weak because of the staff used by Talia, and since we would assume the staff is magic, Superman has an excuse.
However, one thing I wanted to point about WF is that, if Batman is appearing like the main hero in those episodes, its mainly because those stories are more like Batman stories somewhat. Think about it: its starts in Gotham, Joker & Harley, Gotham PD with Bullock and Gordon, Batman of course, and his findings start the story. Sure, its Superman story too, but if you look at it like that, it starts with Batman. Same goes with Demon Reborn, but again because Superman has an in-story excuse, it would have to be Batman's story, and if he wasn't there, someone else's.
This goes back to the sequel: all the talk I've heard is of Superman, which makes sense given that they might be secretive or they don't know to the extent of how Batman will be portrayed. Because of this, this sounds like (and I hope it is) a Superman sequel co-starring Batman, rather than a shared film. Speaking of which, if they were to share the film, let it be both their stories. How to do this? Well there is a Superman/Batman novel called Enemies and Allies, and in it, the situation/conflict is looked up by both Superman and Batman, but separately. They only come together when their cases intersect, as well it's the right time for them to team up. That's an example, but a good one. But so far, it seems to be more of a Superman sequel co-starring Batman.