WB is most concerned with it doing a number that is ...big!
As long as the film's worldwide opening weekend (which this film opens internationally on the same weekend as domestic) is huge, it won't techincally matter how much it does or doesn't do domestically.
If the headline on Sunday/Monday reads "Batman v Superman: Dawn of Justice makes 300 million worldwide on its opening weekend" no one's going to care at WB if it didn't surpass AGE OF ULTRON'S opening weekend.
All this film has to do is make serious money worldwide for the 5 weeks it has by itself before CIVIL WAR is released. If the film is at or close to 800 million before CIVIL WAR hits, it's a success. I don't care how anyone spins it.
Great reviews and word of mouth would be nice but let's get real, WB is looking at the money and as to whether or not they can REALLY go full steam ahead with their shared universe.
The perfect scenario is having great word of mouth, great reviews (70-80% on rottentomatoes) and the box office is pure fire for 5 weeks to the point of a billion five worldwide before CIVIL WAR hits.
But, at the end of the day, measure a film's success on whether it makes a billion dollars worldwide is frankly ******ed.
When IRON MAN 3 hit a billion dollars worldwide back in 2013, I knew then that expectations for each film in this genre, based on which characters were in the film, was going to be trouble. GUARDIANS' sequel eventual success is going to make the expectations even worse.
To me, MAN OF STEEL (especially when you factor in how much it killed IRON MAN 3 in home video) was a unqualified success.