Ghosts are not a safe switch in. Team Preview will give away the fact that you have ghosts so right away the odds of successful prediction are in favor of the Khan player. You keep saying 'you' don't have any problem with Mega Khan... did you ever stop to think you don't actually play at a competitive level? Just curious, where are these Khans you've been fighting? In-game free battle? Pokemon Showdown?I'm just going off what Shadowmario's posts, since apparently I'm not thinking and he is.
The +2 only comes off a successful Power-Up Punch, which I have had no problem preventing with Protect or Ghost-types.
Also pokemon like Ferrthorn with Rocky Helmet inflicts around 14/24th of Mega-Kengaskhan's health every turn, especially usable if you're switching into a Return or Crunch even a Power-Up Punch.
Ferro does 60% damage on a successful prediction and dies the next turn to earthquake/fire attack so you've managed to completely sac your pokemon for nothing. Better run rocky helmet Druddigon too. There you go, countered Khan and it only took two pokemon to do it, you don't even need to worry about their movesets since they wont attack anyway, its brilliant.