It may very well be a conservative estimate, but the box office has gotten very unpredictable - especially as far as superhero movies go.
Thunderbolts proves that a good movie alone doesn't cut it. Deadpool & Wolverine proves that audiences eat up "member berries" -nostalgia- these days.
Where Superman will come out in all of this remains to be seen, but what matters is that it does enough and is well liked enough akin to Batman Begins back in the day.
I've said it time and time again: this movie has a huge uphill battle due to how tarnished both the Superman and DC brands are for moviegoers (not unlike Batman before 2005).