You could do a planet-size-spectrum like that; but reversing the analogy would be - I don't know, some sort of spectrum ranging from "God doesn't exist" to "God exists"? That seems a pretty binary set of points to me - how can the state of "God 50% exists" make any sort of sense?
And with nothing to need God for you can then reject the existence of God.
Similarly, if nothing that you ever see requires the existence of Jim, then you can reject the existence of Jim, right?
The state isn't "God 50% exists" but "there is evidence which indicates that God might exist, but the evidence is 50% as good (or there is 50% as much of it) as the evidence at the far end of the spectrum". There's a continuous line from lots of evidence for God, to some evidence for God, to no evidence for God.
Another month, another rationality quotes thread. The rules are: