Assuming every function is called the same amount of times and carries the same cost it would indeed be silly to cut up a system like that. But in the real world some parts of the system are called more often or carry a high cost of the execution. If you can scale those independently of the rest of the system, that is a definite advantage.

For me the antipattern poses itself when the cutting up into microservices is done as a general practice, without a clearly defined goal for each service to need to be separate.

(And by the way, i’ve seen a talk before of an application where the entire backend was functions in a function store, exactly as you described. The developer was enthusiastic about that architecture.)