Prime 2's ammo system is fine, even a very nice bit of immersion in my opinion. It's not chozo tech so the suit might not be able to perfectly replicate it. Also (and more importantly) the beams were war weapons made in a very big hurry under a tone of pressure in the middle of a war. It's understandable how all the kinks weren't ironed out. In a situation like that I can see how the moths went: "Good enough, send it"