pete-Well, that really isn't the case. Many spirits were assumed minor powers, many were thought of as mischievous and with unique abilities other than ours to cause trouble but not all powerful. Polytheism/henotheism essentially means that there was no all-powerful. Power was distributed around as agents of countless phenomenon. Eventually the philosophically literate had a problem with their deity being less than everything and imagined a single all-in-one God.
You believe that the very first human being that invented the concept of God looked all around at all the things he couldn't explain and all at once attributed them to a thousand different gods despite there being absolutely no concept of God in existence...then much later on someone different said no, it's just one god?
Even if this was true, the inferring by this human lead to a conclusion that it was a group of beings greater than he. Otherwise, he would have been able to explain any occurrence thru his own human experience.