Cost is also a universally effective way to penalize a choice that a given race does not make while, for example, shieldbonus = -0.50 does not.
If the tribe “bonus” was a cost increase on everything—to reflect their penchant for overbuilding everything—then they’d field fewer ships in any given battle. Note that the Tribe-specific modules could then be priced VERY low so that even with the “bonus” they’d be cheap.
I could see the “rebels” paying more for everything as well, whereas the feds can just print more money
Seems like an easy way to introduce “numbers” balance. Note also that because it is hull-based, some designs might be mass-produced and immune to the cost overrides. Some sides might get a cost reduction as well, allowing them to field MORE ships. I could imagine a race that was lower tech, but good at manufacturing, for example. You give all their ships a speed, armor, and integrity negatives, but make everything cheap for them with a cost reduction for each hull. They then field many ships that are less capable.