Batman can beat everybody is one of the biggest examples of being willfully delusional I've ever seen. At least when Morrison does that he does it with an air of absurdity, but other writers/fans have taken this notion to extreme proportions. Yes, Batman is one of the coolest characters ever created and could beat heroes and villains on a comparable level but that does not mean he can go toe to toe with aliens, gods, and incredibly powerful supernatural beings simply because he trained his body and mind to the peak of human perfection. I love Batman as much as the next guy but this machismo his hardcore fanboys have about him is really something else.
If they used New Frontier as the plot(but tweaked everything to take place now) and the Watchmen flashback structure to make it feel like a lived-in universe and have some sense of camaraderie they could very well pull off Justice League without solo introduction films for the rest of the members. The movie would have to be 2 and half to 3 hours long for sure but there's no real problem with that. :)
As for the line-up: Superman, Batman, Wonder Woman, Green Lantern, the Flash, Aquaman, and Martian Manhunter
Villain: The Center or Helspont. This way you could build up to Darkseid.
This is great news for Superman fans. For years I've suspected a large part of DC marginalizing Superman (in both comics and adaptations) had to do with Shuster lawsuit possibly taking away a large chunk of the mythology thus creating a certain bias against Supes from the top down. Now they can let the franchise soar without fear of that happening. Hopefully with a new film on the horizon, top shelf talent on three Superman books, and the 75th anniversary looming WB/DC will give Supes some of that spotlight Batman has been hogging for 10 years or so. Hey, a guy can dream can't he. :)