As much as I love BBEG takes over the world, cartoon villainy also tickles me (as someone who watched a lot of like Kim Possible growing up)
Like imagine he's just terrible at it, at least to start. He's got infinite time and power. Why rush? Savor the journey. You only get to take over the world once and it took so long to get to this point. You don't pop out the ritual doing big takeovers.
Ya know plus if people get lured into a false sense of security that's also easy to exploit later.
Astarion gets so enraptured by finally being able to see his reflection, turn into a bat and walk in the sun he gets distracted and that's like a whole year of time gone.
Obviously, he has to look the part so he'll need new clothes, some portraits, statues ya know the works.
Getting rid of every trace of Cazador (its his mojo dojo casa house now and he wants it his way).
Too drunk on wine and blood to think about how those dwarven artificers are probably conning him. They get another year on the eternal darkness machine and then heads are rolling.
Maybe he's had a long process of trying to find actually competent spawn and developing leadership skills he never had a chance to before. Sure, he can compel spawn to do things, but that doesn't mean they're good at whatever it is he wants them to do.
If Raphael can practice his monologues why can't Astarion?
Throwing more parties than are actually necessary to uncover the secrets of his enemies.
Spitballing plans all the time, but they just go on an idea board.
Some Paladin presumably: "He poisoned our water supply, burned our crops and delivered a plague unto our houses!"
Citizens: "He did?"
Paladin: "No, but are we just gonna wait around until he does?"