This is about watches in general, not just casio.
Unless it's using tritium or some other fancy illumination, the standard type of lume for watches was designed initially for divers right?
It's there for them to briefly pass their flashlight over and illuminate the hands/bezel and to see the data they need to see for their dives.
It was never designed to keep on your bedside table and be legible after 7 hours plus in the dark.
Yet reviewers will still mark down watches for bad lume when it was never designed for normal daily use.