The cameras you can buy used for a couple thousand dollars have essentially the same sensors as huge cinema cameras, if not better in this application assuming you'll take stills.
Professional editors and color graders have to lower the dynamic range, because there is basically nothing that can get as bright as, say, the sun, and because basically no display can sustain peak brightness over the screen, which introduces an EOTF transfer curves, reducing the peak brightness and thus dynamic range.
You're right about pirated films, but that's because they're typically recorded in a run of the mill cinema while it's playing, not in controlled conditions in front of a carefully calibrated screen-camera combination taking a photograph of every frame.
