That proves only that an armed helicopter in a target area is a danger to a fighter unaware of his presence, not that a helo with a couple heaters is even remotely capable of performing a DCA.
People may knock the Harrier dudes for carrying AMRAAM and Cobra dudes for carrying AIM-9s trying to execute DATF, but what's the alternative?
I don't have a dog in this fight (note no wings) and I'm just trying to improve my overall knowledge of your warfare, but from reading whats been around it seems, and as originally stated when it was brought up, its not so much as Cobras and Harriers are being intended for air to air or really even relied on for it in the scenarios mentioned, but its more to give the ARG or the CAS assets themselves more of a fighting chance if a couple of attack or fighter aircraft did show up to play. Its not like either attack A/C would be able to evade a fighter A/C effectively, so doesn't it make more sense to stand the ground and put up a fight (or some resemblance of that)? Ultimately I would think the best scenario is early warning is effective and that a true air to air asset could get on station in time (unlikely but ideal), but as Treetop mentioned, if your going to go into it with the mindset of what's the point if its unlikely, well then what's the point of performing any mission? Even so wouldn't it be better to have AV-8B's performing CAP over an ARG than having no CAP at all? Why do I have to carry around 9mm if the threats in the area are equipped with RPK's, PKM's and things that go boom and its me against 30 of them? At least I'll be able to put up some sort of fight long enough that a reaction team might get to the show and take a couple of the lunatics with me. Just my uninformed line of thought, so bear with me.