Siege equipment should only be able to...
A lot of that “blind firing” isn’t actually blind firing, but done with a spotter, or the siege operator has a very good idea of what they are doing. You know, like a lot of artillery from the real world, from catapults and trebuchets to cannons, mortars and howitzers.
The only siege weapon in game that should even be considered for some sort of LOS requirement is the ballista (which is already accounted for), or maybe the Arrowcart, seeing as how the Arrowcart is so incredibly easy to aim. But as for actual siege weapons that fire in an arc?.. nope, not going to happen, that’s how those siege weapons actually work.