I think there would be a lot of plummeting indeed
As for F4, one thing is certain, if it were up to the director we would have at least have a different superhero movie, the studio made it a generic bad bull. At least Josh Trank could have failed nobly with trying something new, I can at least respect that a bit.
Also Deadpool is getting a release in February which will probably be a good thing since it shouldn't have much competition, maybe it will end up as Kingsman. Though I really can't check what exact movies are showing on the same weekend.
EDIT:
It's facing
• How to Be Single (WB)
• Zoolander 2 (Par.)
• Barbershop 3 (WB)
• Shut In (EC)
Kind of funny we have four different comedies counting Deadpool, that might be very troublesome, though Deadpool is also rated R and the ONLY action movie so that might give the extra boost and I guess Dakota Johnson's stardom isn't that big after Fifty Shades of Grey but still the name of the movie alone will steal all the female audience.