So what you're saying is... the lore is a bunch of inconsistent garbage. None of this explains how the divine realms work, how portfolios operate within those realms, how Divine Casters like Clerics, Druids, Paladins, and Rangers utilize this force. Arcane is a bit of nonsense, but at least there is SOME explanation. Now divinity is just the nonsense of belief, will, and randomly assorted divine portfolios? Regardless of the actual status of the entities? Or awareness of the caster, for that matter.
Tempted to insert the "always was" meme.
The thing you might know about deities already, is that in the realms they AREN'T immutable. Portfolios usually take precedence over individual beings, which is why we can have deities getting squashed together into one, or have one deity getting split into two, as major events that change the world occur. Splitting portfolios, or making new ones, can also happen, which is why we have Angharradh, who is actually three separate deities, including one that was at one point an aspect of Akadi, who is a primordial, who later spilt and became a lesser deity of her own.
The Bhaalspawn from the first BG game were created during the Time of Troubles, which is when the overgod Ao got sick of the gods being powerhungry arseholes and gave most of them some time out in the material plane. Lots of gods died, were subsumed into other gods, and a couple of mortals even ascended into gods by being given (or taking through force) their portfolios.
