I disagree, I think headphones differ greatly in how well they can reproduce sound dynamics. In fact, I have no doubts that I can clearly hear differences in dynamics between headphones and that RE0, in particular, has an obviously limited dynamic range reproduction capability compared to many other IEMs and headphones. Of course, recordings can differ greatly in dynamics as well, and I agree that recordings can have much greater variations in dynamics than headphones. However, listening to music with a wide dynamic range, like a well recorded classical or instrumental can reveal great differences between headphones in this area as well. With RE0, I felt that dynamic music sounded quite a bit flatter and less expressive than it should - the variations between louder and quieter sounds became far less pronounced and exciting.
That's a result of it's frequency response,not dynamic range. IEMs don't simply have their own dynamic range, any engineer will tell you this.