Just because you don't like a certain act doesn't mean they're not big enough for the slot they're booked in. LG is a boring, dull headline booking but he is definitely big enough when you look at his tours, selling out Heaton Park, etc. There is absolutely no reason that he won't be back next year unless he decides himself he doesn't want to.
That Stormzy shout is ridiculous too if you're trying to claim that this time next year he won't be headline status. In a few years time maybe he'll fade a bit but you can't make the assumption that he'll drop off a cliff so quickly with no real evidence.
I think we'd all like to think someone we think is a wasted headliner will be replaced but realistically, that's quite unlikely. Throughout the rest of the lineup there could definitely be a lot of shifting around and new inclusions + removals but in terms of headliners I think it's quite unlikely. Wouldn't mind being wrong like, someone more interesting than LG would be quite nice. Just read this back and I don't mean it to come across rude or attacking or anything, just my opinions of course.