If your planning on going >20 mounts, you probably want to lean on energy weapons, and large ones at that. CERPPC with capacitors, CERLPL, etc. Reach, accuracy, high per-mount damage, and a lot of the mass that would go into fire control calculations offloaded into heat sinks (which dont)
A case can also be made for at least some long tom cannon - despite their mass, they are notable for being extremely effective as against reflective armor - which should be common on aerospace fighters, given that most of its drawbacks dont apply in that context. (If your Aerospace fighter is getting punched, something larger has gone wrong)