I think plague bombs were disallowed on drones because it was thought imbalancing. PBs have a range of 5, which knocks their chances to hit a planet down to around 950% at max range. It's unlikely that they'd be destroyed before entering that range, since hitting drones with -50% to hit is just a bit harder than hitting a planet with +1000% to hit.
Do drones use 200 supplies/turn, or 200+fuel/turn?
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The Unpronounceable Krsqk
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Freefall