According to the same wiki that you linked, Azuth has been separated from Asmodeus since the Second Sundering (1486 DR) - BG3 takes place somewhere 1494+ DR (if I understood things correctly). Sooo, Azuth is already a full-fledged individual again.
Either way - correct or not, I do very much like your post in general.
I am new to the FR lore as well, but I been digging massively (similarly to yourself, I'd presume
) to emerge into the amazing universe that is the Forgotten Realms.
And, while i do not think that Gale might be Azuth himself - I VERY much agree that there is something odd about him and I am 100% certain that there is MUCH more to him than what we've seen so far. I'd recommend you check out the earlier conversations here regarding Gale's potential story - there is a lot of interesting things that people have found, just like the stuff you've noticed!
