This is a great discussion!
Over time, DND cosmology, and the worlds that inhabit it, have gained nuance. I think Paizo has done a better job of it overall, compared to TSR/WotC, who mostly hand wave it. Paizo has several products that tell a possible origin story to entities that start as one thing but evolve to something else over eons. IIRC, it’s an origin of Asmodeus, who is a deity in their world of Golarion. No reason to assume that it couldn’t have happened for all deities.
I’m going to counter that with this one
One Bad Decision
That’s when Miko decided to end Lord Shojo. That one decision cost her the LG afterlife.
I suppose we could argue how close she was to losing her paladin/LG status at that point and this was the tipping point. We could discuss if each action “weighs” more heavily on the actual scales, which we have seen with Roy.
I think it’s worse than that. Probably 98% of the population, including all sentient beings, live their life and have no interaction with anything except clerics/priests who preach to them. I would think that makes them more neutral. I mean, how many of us have an opportunity to do something really Good (LG) or really Evil (CE)?
(Digression. I went looking for a word so I didn’t have to use “really” as an intensifier but nothing I found worked. (Excellent, Fantastic, Astonishing, breathtaking) Maybe Exalted and Vile?)
Then you have the 2% that do interact with and know about the afterlife and they still take risks! Heck, a lot of this is Roy stopping Xykon due to Eugene making an oath to that effect!
One of the bad ideas of Forgotten Realms, was the Time of Troubles. FR does have an overgod that sent all of the deities of the Realms in avatar form to the Realms. If they died there, they were gone for good. It was said after that, deities would have power based on their worshippers. Fortunately, I think 3E did away with that nonsense, or otherwise (for the Realms) Chauntea, goddess of agriculture, would probably have 70% of all power. Then the evil gods, like Bane, Lord of Tyrants, would have next to no power! Equally, same for Tyr, Lord of Justice. That is due to my thought that most people aren’t extreme and just want to live their lives.
Thanks for the discussion!