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Yes, I think the range of point-defense weapons is a bit extreme. It ought to be comparable to the range of fighter-based weapons (3 or so) and not much more.
An anti-missile is an interesting idea. It's true that an interceptor missile could be smaller and faster firing than a ship-damaging missile, so maybe this is something you could add and test out. If it moved pretty fast (speed 5 or 6) and had a range of at least 10 it could be a good substitute for "area defense" as it is currently handled by PD cannons. But the delay between firing and hitting the target could make quite a difference in it's performance compare to PD cannons.