I agree with you that 10X managers exist, but it's utter nonsense to claim that 10X developers don't exist. I've met people who are possibly at the 100X level; it's worth remembering that some tasks cannot be done by an average developer with any amount of time.
I imagine that there are probably tasks that don't allow the 10X or 100X to show through; anything basic and repetitive enough (or so heavily specified that the developer's job is essentially "typing").
100X developers can straightforwardly - sometimes - find solutions to problems that are simple, elegant and fast. This often means that the things that they do are not only cleaner than the solutions produced by weak(er) engineers, but also require less complexity to implement them whether at the organizational level (e.g. because the task is being done by 1 person in 2 hours, rather than 4 people in 200+ person hours, there isn't any time spent on meetings) or at the technical level (e.g. because the task now runs better on a single computer, rather than a cluster or threaded machine, it no longer requires parallelization and a distributed system).
Sometimes this also comes about by a deep knowledge of available algorithms and systems, so while a naive programmer might start flailing around like a dog with their head stuck in a bucket, an experienced person might recognize the problem as an Integer Linear Programming case, etc.
There are plenty of cases where no-one is 100x, of course.
I imagine that there are probably tasks that don't allow the 10X or 100X to show through; anything basic and repetitive enough (or so heavily specified that the developer's job is essentially "typing").