The point is to tell an exciting story - there’s no right or wrong definition of what that means for you.
The dice’s purpose is to take you down paths you might not have chosen deliberately but the goal is still to have an exciting story. If the DM wants to be like “I recognize the dice have made a decision but given that it’s a stupid ass decision, I’ve elected to ignore it” then he has my full support.
Maybe a cleaner way would be to decide up front: which outcomes am I ok with? and simply cap the roll at that. You know the paladin only has 17 HP left and you don’t want the paladin to go down so the maximum roll you want is 16. So if you have roll 4d6 damage. You do: roll 3 roll 8 roll 12 roll 18 16.