Separating charged/uncharged melee and putting uncharged melee same button on finisher is not prioritizing a finisher.
What is happening instead is I will always do an uncharged melee and will only do a finisher if the target is still alive [i]then[/i] I will do a finisher. This has led to me needing to reverse all of my rebinds to do any sort of bounty involving finishers.
I am on console so don't have the option to create a second binding or whatever the PC fix is that's floating around.