About balancing by rarity, are railguns really that rare? And even so it still stacks up awkwardly to the light autocannon types.
Also I always viewed rarity as being more related to concentration of force, which just tends to be naturally better later game.
For example with ships, if it's all I had I might rather have 2 lashers than a scarab or 4 lashers than a hyperion. But as an escort in a late game battle I'd generally reverse that order. Or even just scaled up - 40 lashers vs 10 hyperions is a different story.
And with weapons the more rare ones are specialized somehow - burst damage, long range, etc. Frequently useful specializations so they're better weapons because of that. And they consume more OP in a slot for something that's likely to be considered better.
But usually you pay more deployment points or OP for something that's generally more useful as a result of concentration of force or specialization (antimatter blasters may be more useful than IR pulse lasers, but they aren't just better in general). Having the railgun actually cost less OP kinda goes against that - especially since the less OP results in it being more flux efficient if you put it in a slot that isn't firing often once you add a vent.
I really like the idea of using clunky bit autocannons, but I just haven't been able to justify it much over using mid slots for even just heavy mortars and small ones for railguns, even pretty early on.
