In and of themselves, beam fighters can come out ahead against AMM spam.
Roughly, a typical NPR AMM ship of about 15,000 tons will mount 20x size 1 launchers plus deep magazines for 70ish salvos. A single 500t railgun fighter at the highest achievable speed (up to 4x racial tracking, of course) is usually going to be able to shoot down one equal-tech AMM in 3-4 shots, so 20x fighters or 10,000 tons will be able to match this 15,000-ton escort cruiser design.
The complication comes from the fact that these fighters usually are operating from a carrier, so for 10,000 tons of railgun fighters you can nominally assume 30,000 tons of carrier as a first estimate, plus the usual selection of carrier escorts. On the other hand, rarely is an NPR fleet made up principally of escort cruisers, so the tonnages are likely to roughly balance out depending on the details of the fleets involved.
The bigger challenge is likely going to be any beam escorts in the enemy fleet which can probably deal a lot of damage to a fighter swarm even if they suffer from poor targeting. 10cm railguns do not penetrate armor effectively at all so you will be doing a lot of sandpapering while enemy beamships can probably take out a fighter with a single hit and will be limited mainly by number of BFCs.