No-one can say that Father Christmas or the Tooth Fairy don't exist. They are both hypotheses awaiting definitive proof.

No-one can say that x or y don't exist.

They are both hypotheses awaiting definitive proof.

They are not hypotheses. It's very tempting to characterise vague or fanciful notions as hypotheses, but if the term hypothesis is to mean anything at all then it must meet certain criteria. A hypothesis is a proposition which attempts to explain an observed phenomenon, and it must be able to submit to scientific testing. Generally, we are talking about issues that have been observed but which cannot yet be satisfactorily explained by current theories without further investigation. Father Christmas and the Tooth Fairy are fabrications (don't tell my kids, even though they're both over 30) which are not based on actual bona fide observations. As a confounded atheist, I'd put the existence of God in the same category.