As a test, I spawned fifteen (15) Avatons directly above some village farms. The avatons summoned their wetas. I left the game for the whole night, to see that only 9 or so crops were actually damaged by the time all the avatons burned up. The wetas tended to wander off and munch on grass instead of prioritizing the crops, and even then, they barely destroyed any plants.

In my opinion, I think summoning 15 sheep directly on the farms would have been more damaging, as they would have trampled all over the crops. I think a creature like the avaton that is specifically designed to be a plague-bringer and destroyer of agriculture should be more of a threat to farms - let alone in large groups.

If balance is a concern, perhaps a config option could control how often wild wetas look for crops to munch / how fast they can "mine" the crops to break them.

Before and After