our character could say some line showing concern and an animation making the move to go after him, but Karlach dying draws our attention and stop us.
Yes, This makes perfect sense.
the romance with Spawn Astarion feels neglected.
And very much so compared to AA.
I'm very grateful that Larian implemented his scene about cheating with Mizora, but honestly, it should have been there from the start, because AA version has always been there.