I guess the dead three are looking for a no limits approach to godhood, Shar could not provide that. Maybe both are toying with involving some far realm entity in the affairs of Faerun?
The main issue with having Bhaal or Shar, or Vlaakith, act as an ally of the absolute, is that you can play a cleric of one. So here you are, a powerful evil deity running an elaborate scheme to gain more power, while one of you lowly level one acolytes is doing their best to ruin it? Which the player character can do, even unknowingly.
At the beginning of BG1 one if the big hints is a book about the dead three your character is given. So now I've been looking at the books in BG3 and there are some interesting tomes, e.g. The unclaimed, about a forgotten cleric of Shar. The book ends with the following lesson ”That not of forgetting, but being forgotten." I wonder whether it's therefore not something long forgotten making a comeback here, which only the truly old ones like Shar would remember. Don't githyanki build their cities on dead gods (my gith wizard claimed sth like that in dialogue)?
