Other ECS implementations might not, but Bevy does come with a system scheduler.
That's an ecs data structure and a system scheduler. If I make a vector and a system scheduler, vectors don't suddenly have system schedulers, they are two different things.
You register systems (functions that operate over the components)
That's just adding a function pointer to a field.
> That's an ecs data structure [...]
ECS isn't a data structure tho, it's a pattern. You must be referring to the component storage. That's, at best, half the equation. You do realize the discussion is about the 50MB program, which uses both the component storage, the system scheduler and other features, right?
> That's just adding a function pointer to field
Just as much as creating a new process, through the IP/PC field in the TCB. Don't know why you focused on that particular point, but sure.