Unless it was something truly horrendous, John being sacked over one comment made years ago seems heavy-handed. If true, I suspect the producers wanted the chance to completely revamp the presenting team and needed a way to push John as he wasn't jumping.
I just hope the new faces of MasterChef are people we can be rude about on the threads. Someone too inoffensive would be dull.
I like Giorgio Locatelli, Michael O'Hare, et al (in fact, there are loads of chefs from The Great British Menu I like and would like to see more of) but I suspect it will be hard for the BBC and production company to find any chef, particularly male chef, from a solid restaurant background who is completely squeaky clean and doesn't have a touch of the Anthony Bourdains about them.