Of the two, I say gunnery is useless without ACM. That means all you'd do is HO, extend, turn, HO, extend. We see enough of this in the dweeby newbies.
You need a small amount of gunnery. Even BAD shots can still get kills. You just need to get in close. To do that requires more ACM than gunnery. If you get a shot and blow it, the way you get a SECOND shot is to reposition. To do that you need to know how to fly your aircraft.
So gunnery does nothing if you can't fly worth a crap.