You made choices and got the results of those choices. The alternative results are different.
!There are multiple endings where Karlach survives in different ways. Shadowheart’s story has at least three possible outcomes, maybe more that I haven’t seen. This goes on and on for each origin character. Even NPCs you encounter in Act 3 are shaped by your choices earlier in the game.!<
Frankly, based on your description, it sounds like you made a bunch of lame decisions. There’s neat endings and then the middling one you got.