uhm, exactly? Quoting a fragment of my post on the first page -
Yet every single Baldur's Gate encounter you mention is exactly that. Barring Mellissan. You don't even LIST Sarevok or Jon Irenicus so actually plot-backed BG bosses don't get your preference it seems.
I didn't list them because they were the whole point of the game. We are talking about bosses that aren't the main antagonists, or am I misunderstanding? Melissan isn't the point of ToB though, so that's why I did list her. She was just a middle-man in Bhaal's grand scheme. She's just incidentally the last boss.
Just to be clear - I'm not saying any bosses in the Baldur's Gate series are well-written, just presented well.