I think you are ignoring the fact that not everyone has ready access to synthesis or the associated materials for it. Horizons is a notional pre-requisite and the OP's suggestion need not be dependent on Horizons.So are trying to convince your self and others that the Basic Synthesis is not replenishing ammunition? It does and it uses Common easy to get Minerals.
We don't need an Ammo Tank. If you want to stay out in combat longer start use Synthesis and start mixing your weapon build some with lasers. Or if you want to stay out forever then use lasers only.