I think one important aspect for the usefulness of general principles is by how much they constrain the possible behaviour.
Knowing general physics for example, I can rule out a lot of behaviour like energy-from-nothing, teleportation, perfect knowledge and many such otherwise potentially plausible behaviours. These do apply both to bacteria and humans, and they actually are useful for understanding bacteria and humans.
The OP, I think, argues that FEP is not helpful in this sense because without further assumptions it is equally compatible with any behaviour of a living being.
I think one important aspect for the usefulness of general principles is by how much they constrain the possible behaviour. Knowing general physics for example, I can rule out a lot of behaviour like energy-from-nothing, teleportation, perfect knowledge and many such otherwise potentially plausible behaviours. These do apply both to bacteria and humans, and they actually are useful for understanding bacteria and humans.
The OP, I think, argues that FEP is not helpful in this sense because without further assumptions it is equally compatible with any behaviour of a living being.