The lore is that the saarlac actually keeps you alive while digesting you. Like, it puts roots in that act as life support so it has a constant source of protein or whatever.

That makes as much sense as The Matrix using people for energy. You can’t feed people to keep them alive and get more energy out than just digesting (or in the Matrix burning) that food for energy.

I could be wrong, but I think the original idea for the matrix was that they were using human brains for processing power and not energy. But someone in the movie making process decided people wouldn’t understand that and instead went with the battery analogy.

Morpheus is the only one we ever hear the battery analogy from anyway. He might well be wrong about that interpretation, and the brain processors are what’s really going on.