Why should carrier combat cost resources, when no other ship has that problem? Also:
Sins has a less than linear economy. As players expand, their increased income from units and research is cut down by increased fleet research, and the distance from the homeworld. The end result is that even with a sizeable empire, it's very difficult to get more than twice the resources you have early in the game.
Now make strike craft cost a FLAT amount of resources. Guess what happens? Carriers become useless. The first carrier might be cheap. The second, third, hell the 10th one may be cheap. But after that, your empire needs to be exponentially powerful to go past an absolute TINY number of carriers, because they're going to flatline your economy in seconds. How is putting a "hard cap" on the number of carriers going to fix things?
The problem with JUST anti-matter is that even if the Light Carrier's AM is nerfed so it'll actually matter, it is STILL ESSENTIALLY free.
No it isn't. Antimatter costs valuable TIME. Push a devastated carrier fleet, and they won't have the time to stop you. Problem is, AM restrictions cost carriers very little time. Even dry carriers can jump around quickly, rebuilding squadrons with ease, and have the additional cover of a fallback position.