I'll clarify.

The cable machines are efficient because they _do the work_ of performing a movement for you, much like how LLMs do the work of writing an e-mail from a prompt describing what you want to write.

They are designed to only activate the target muscle/muscle group during the movement, which is good for working that muscle but bad for working all of the other muscles that _should be_ activated in the kinetic chain for that movement.

That's the metaphor I was trying to convey.