ruralair, your post's final paragraph is concerned about sky mantas at night.
If Supply is updated--which I doubt--such things will only exist there.
The drops of mantas will likely be eagerly sought, much like wither skelly heads--because what we really want is a Mega Manta! Something with a great drop, equal to a nether star.
On the other hand, if sky mantas are similar to temple guardians, doing sonar damage from afar, then I agree with you. Such a damaging ranged/witchery attack could ruin the night for most players.
Working underground or inside of buildings is not a big inconvenience. I look forward to night hunters flying to battle the mantas. Seems fun, unless it's in Insania.
Insania mantas would be epic.