It's a legitimate complaint, and one that's going to become a bigger issue going forward. A lot of movie stars have compensation that's at least partially based on box office receipts, so anything that cuts in to that market cuts their compensation.
I assume there will be a contractual shift to eliminate that type of percentage based payment in the future, but that means the upfront cost of producing these films will increase when they're having to pay someone $20 million regardless of how well the movie performs.