I hope we see more of this story, as it rocks!
One problem could be that in a crux story once the chicks are on the sticks there is not a lot of action, just a slow painful death. A solution could be to introduce drama around the cross rather than on it. A pitched battle around the crosses would be an interesting diversion, with getting caught in the cross-fire (literally!) adding to the usual perils of the cross.
The slaves might be angered rather than intimidated by the crucifixions, and attempt a mass escape or riot. Probably not going to go well for them, but if lots are killed it eats into the profits of the operation.
Friends and relatives of the captured girls may try to rescue them. Primitive does not mean stupid, so no frontal attack. Stealth and luring the pirates into ambushes are more likely. Maybe they have old technology from the colony ships that brought them to this world? The "Old Tek" would be revered like holy relics, but would give them an unexpected edge.
The slavers themselves may not be a monolithic faction. One group may try to seize control of the whole operation, or just decide there is more profit if shared among fewer people. They might just fall out over girls or money, and the fight gets out of hand.
The long arm of the law might arrive on the planet. These pirates may act tough, but when the Colonial Marines in power armour show up they are going down. Or the cops just collect heir pay-off and depart!
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