I remember people laughing at my AVATAR prediction when TRANSFORMERS: REVENGE OF THE FALLEN opened to big numbers. The same thing happened when THE TWILIGHT SAGA: NEW MOON opened. I held on to that belief that AVATAR would win the year even after its opening weekend. Then the second weekend happened, the third, the fourth, the fifth, the sixth, the seventh, etc... lol
Again, I don't think it's SH fatigue. It's just that DEADPOOL, BVS have satiated the demand early. It's not like people are tired of seeing these films. They simply just don't see themselves spending for every movie of the genre. ZOOTOPIA and THE JUNGLE BOOK have been performing well as well. A family of four won't see every family film out there especially if they are just within weeks from each other.
BVS was actually lucky to be released earlier than CA: CW. If it was the other way around, the numbers could have been worse.