Quote Originally Posted by Razushu View Post
pet/npc AI sucks across the board. I don't think spirits were mean't to be near the power or match the utility of avatars, lord knows what SE initially had in mind for them but it's safe to assume they decided against and left them as they are now
I'd bet SE simply didn't think of efficiency. They thought "And the SMN can assault this spirit, and it casts some random spells. It will be funny!"