It would be completely arbitrary and clearly motivated only by saving the appearances, but yes, you pretty much need a hard fundamental limit to explain why they are so epiphenomenal despite such cosmic resources. There’s no plausible story where they can manipulate the mortal realm enough to screw with pilots but also we observe the universe exactly as it is. (And the easiest hard limit is simply that, like regular aliens, “they don’t exist”. It is hard to change the universe noticeably when you don’t exist.)
It would be completely arbitrary and clearly motivated only by saving the appearances, but yes, you pretty much need a hard fundamental limit to explain why they are so epiphenomenal despite such cosmic resources. There’s no plausible story where they can manipulate the mortal realm enough to screw with pilots but also we observe the universe exactly as it is. (And the easiest hard limit is simply that, like regular aliens, “they don’t exist”. It is hard to change the universe noticeably when you don’t exist.)