By the rules of the game you can’t surprise someone who is aware of your presence, so you’re correct.
That also means you don’t automatically get to interrupt a monologue by blasting the bbeg in the face mid-sentence. You need to roll initiative to see if you are able to act before they can respond.



Yeah, absolutely. There are plenty of RAW ways to allow a bbeg to monologue, at least to some degree.
Of course it’s also entirely within the GM’s power to just tell the players to let it happen, but it definitely feels better when there’s some kind of in game reason why.