I have to side with trump on this. The first Fox debate was ridiculous. Megyn Kelly was merely the most obvious problem. They were totally in the bag for Bush and desperately trying to tear Trump down. It's the same thing we complain about with the liberal networks, ie all the others.
Republican candidates don't have any real leverage with liberal networks or cable. The situation with Fox is more complicated. Most of the candidates totally depend on fox, but Trump is so powerful, he has leverage over Fox. His supporters are their core audience.
Fox's statement mocking trump was totally unprofessional. Would they ever do that with Obama or hillary? Not on your life. He had no choice but to withdraw after that. Anyone who watches Kelly's show for 15 minutes can see that she is obsessed with Trump and burning to take him down. It's very unprofessional. Hannity by contrast has played it down the middle. I have never been a big fan of his and I liked Kelly, but she has seriously damaged her brand and Fox in the process. Ailes and Fox are in a tough spot, as she is their big new star and they can't just ditch her, but this is really hurting them with their core audience.
By contrast, it doesn't hurt Trump at all. Any debate is a risk for the frontrunner. Trump again dominates the coverage and makes the other candidates look insignificant. Perception matters.