It isn't great. I don't think anyone is going to disagree with you. But you have to factor in that the other 2 movies are overperforming. Man of Steel can't make 50m this weekend if WWZ is making close to 60m and MU is making 80m plus. I think the Man of Steel number is misleading.
I think it will still do at least 45m. And it may look bad for MOS, but WWZ and MU overperformed and took a lot of the box office away from it. I personally don't see WWZ having good legs.
As I said, it was always going to be a tough weekend for MOS.
You can't really judge Man of Steel's legs yet, because it's had to deal with the NBA finals, and with MU and WWZ opening up on Thursday. I say it's held up pretty well.