I think one of the big issues with the Bradley Cooper scene is that he was a last minute replacement of the original actor and shot the scene by himself on a green screen and then was superimposed into the scene. I'd also say that in LotR, the hobbit scenes where they're mixing with big folk got a lot worse in the last film (like when they're dancing on tables after the battle of Helms Deep) when they were doing that instead of using practical lens effects.
I thought the parole board halfling (gnome? I thought I saw pointy ears), fit a lot better into her scenes, and wasn't nearly as distracting.
I missed that Bradley Cooper was a digital replacement for the original actor. That would do it.
The more Jackson's Middle-Earth movies relied on digital green screen and less on forced perspective and body-doubles, the less convincing their interactions and presence with the rest of the world became.
Agreed, the gnome felt less jarring.