Well, that could be one way how the first religions formed--though I suspect there were often very drastic and sudden changes, as well--but I don't see how this supports your claim that one cannot conceptualize a god without reference to a preexisting religion. You still have the "first mover" problem; how do those first practitioners conceptualize a god without reference to any religion?
In that scenario, those first practitioners would probably be unrecognizable to practitioners many generations later.
In that scenario, those first practitioners started out with something small, a particular idea that was neither controversial nor especially detailed, one that may even have gotten lost or marginalized over time.
In that scenario, the idea of "God" may not have been present at first at all, just some aspect of it, such as "mystery" or "great power", and it was through later developments that a more compact idea of "God" was developed.
In this scenario, there is no first-mover problem.
Non-sequitur.
You'll need to explain this one.
People who have been born and raised into a religion will likely have a much different grasp of it than people who haven't.
It has nothing to do with being sure of myself. I'm sure of the evidence. You can't seem to grasp the notion that truth doesn't have to have anything to do with ego or confidence. It exists independently of that.
I'm sure that one needs to be sure of oneself in order to be "sure of the evidence."
I don't think one can grasp the truth without also having enough ego and confidence.
The op has a similar outlook -
How much trust and knowledge of oneself does it take to be able to tell what is what? It takes a lot for me to trust my own senses, but I tend to give a lot of weight to the physical types because they are bound to the physical realm as is my body.