Maybe a balance thing. But the default light art. ammo is way to low damage to use. If you hit a biter nest with a few artillerys it heals faster then you can damage it.

Maybe use grenades and unlock it with mil tech that way instead of a water barrel change it to 2-5 grenades? That is also more "logical" as you are just shooting grenades through the artillery then. And then later upgrade to true big bore artillery when you get yellow science.

(Or make a mid-tier shell using grenades for more damage?)

The mod has several tiers of ammo. The idea for the first ammo is that you need a dozen plus artillery guns focus firing a single nest to slowly bring it down. It is designed to be a resource intense solution; and the more you fire at once the less regeneration you have to fight. 💪