TLG automatically picks its mode based on your tv. If you want to run super sampled 1080 version with better performance, you have to change the Pro's output to 1080p in settings before starting the game. Apparently 1080p mode uses the TVs upscaler to fill a 4k screen, so if you want the better hardware scaler you can switch the Ps4 Pro's output back to 4k after you are running the game (supposedly the game doesn't check your output after you start playing).
It's really dumb, but hopefully they will patch it.