I'm not sure where I fall in this discussion, but taken as a whole, point defense should -lose- to an equivalent resource expenditure of missiles and/or fighters. Why? Because otherwise it's a stalemate and if both sides take loads of missiles, fighters and PD, nothing ever gets hurt, and that makes it a boring game. Generally, if (for a roughly equal amount of ordnance points, fleet points, etc) you can wait out the missiles until they run out of ammo, PD is probably too good.
That's not saying that PD should do nothing, and if it's not doing -enough- right now then that's a problem; the lower end of energy PD certainly seems a bit meh, and I never even see anything with a Guardian so I'm not sure they can be usefully considered. In general, PD should be a way of extending the survivability of things when faced with missiles and fighters, rather than a way of countering them entirely - the way to counter them entirely is either interceptors to kill opposing fighters, or blowing up whatever's launching the missiles.