Yeah, "missile launcher" would be good enough, as there aren't that many ASMs in FS universe. Just the Fusion Mortar and VFC, I think. The latter is never used anyway, and the former is restricted to Fenris/Leviathan.
Light/Medium/Heavy/Main would be my choice for beams. Light=S and below, Medium=Slash, Heavy=B/L and Main=BF/LRB. Laser Turret for blobs and AAA Beam for, well, AAA beams. Flak Turret for flaks. Now that I look at it, in the end, the rename would mostly concern beams. TBH, we could probably get away with just designating AAA beams. Besides that, the current FS system of Laser/Beam/Flak/Missile works quite well for canon ships, IMO.