It's something I've consistently heard both by fans and creators that the X-Books are hard to access for the other Marvel writers due to the X-Office being under some kind of iron fist (and I'm not talking about Danny Rand). This creates the feel of a partial disconnect, which varies over time, but the X-Books tend to be mutant-centric with less use of General MU appearances compared to others. I tried googling how exactly it was, but didn't get an answer, so I'm asking here as I'm sure I'll get one.
Just how tight is the control on the X-Books compared to other Marvel titles? What's the exact cause of this?
Here's a hypothetical scenario:
I'm a writer of a Spider-Book, and I want to have some mutant characters appear in the book as more than just some background filler. They actually interact with Spidey and bear on the current plot, taking place in both sides' status quos. How hard would it be to get the approval of the X-Office to do that?
If anyone has solid answers, please say so. Thanks.