Those ballista were just a bit OP. Semi automatic. Recoiless. Presumably rifled as those bolts flew dead straight. Must have been gimballed as weren’t affected by pitching of the boat. 100 percent accurate at picking out high altitude moving targets. No ranging shots needed. But that could have been because the bolts were unaffected by gravity so no ballistic trajectory to worry about.
Stealth tech included on the ships too.
I can see why they weren’t too worried by all those ballista on KL at the end though. They would have hit Doorne before they hit a target 50 feet away. While she’s waiting for Jon Snow to arrive, Cersei should start raining artillery down on Winterfell.