I think, if handled right, that JL can put up very big numbers. Maybe not 2B numbers, but certainly Avengers/JW numbers. I also think you're right when you say that BvS is a key movie for DC. I hope the upcoming stand alones are good too. We don't need another Green Lantern like the last one (although I kind of liked it even though I recognized it wasn't what I would call a GOOD movie).
I think IW, if good, could "maybe" put up 2B, but that's a LOT of tickets. The only reason I think Avengers will probably do a little better than JL is that it's probably a little better known than JL (EDIT: I'm talking general public). It's had a chance to develop its brand. If JL is really, really good, all bets are off. Sky's the limit.
Neither is really in the SW stratosphere. I think it'll come back to earth a little bit in Ep 8 and 9. TFA went crazy because we were all dying for a good SW movie (and, IMO, we got one).