I'm pretty sure there was a datapage somewhere that said there were 1500 mutants now living in Avalon, or something. And I'd trust the traumatized Brian over Jamie any day, just let someone else do the actual ruling. Or hell, Betsy, just have someone do the day-to-day stuff while she goes out being Captain Britain. Lots of kings have done just that.

We HAVE seen Jamie seemingly kill people for little reason than his own amusement. I wouldn't be surprised if he HAS done some major shit and covered it up, he's certainly powerful enough to.