*Uses grappled to latch onto his legs and pulls him to the ground* "Nice to ya Moloch now lets see if ye can fight without yer fancy jet pack." Yeah but we might want to actually take over the planet before we focus valuable resources in converting a single hive city out of many.
To do that you would have to not only convince our lord but his four other lieutenants two of which would much rather recruit more soldiers and kill everything else and move on to the next planet. You need to think realistically about your current goals.
You can still do whatever to the hive city once you conquer it but have fun convincing the Khornates to leave survivors where they march.