Profound Sayings That Are Junk

I agree with the gist of your post, but one saying that is very true is that "postulates shouldn't be multiplied without evidence" (Occam's Razor, or one version of it). So proposing the existence of beings for which no evidence exists is unnecessary and unlikely to be true considering such possible beings are only limited by our imaginations, and we can imagine far more things existing than what things actually exist (and some things that exist may be beyond our imagination). This is especially true when the reason we postulate them tends to come from our anthropomorphic biases that are provably unreliable. So what you said about God could just as easily apply to any mythical beings.