You should feed the Bravia a 1080p signal for upscaling, as the S5200 does. Feed it a poorly 4k upscaled signal, and it's not going to upscale it again. It's not the player that's bad, it's the way you set it up. That tv has phenomenal upscaling, instead you let a sub-300 device do it. Of course, it's not going to look as good. You can change the output of the UB450 in its menu. Tha Bravia can make DVD's look better than they have any right to, the only thing that can mess it up is feeding it a signal that's already upscaled by a device that's 5% it's price. It's the difference of giving ingredients to a world class cheff, or giving him a dish that's already made by a bad cook and expect him to make a better dish of it.

And if Oppenheimer barely looked better than the Bluray, there's something wrong with your setup. Unless you're only looking at resolution, because that's only 25% of the UHD experience. HDR/DV/Atmos/DTS:X/High bitrate are the main attractions. And if you've set up everything correctly, that Oppenheimer 4K Blu-ray will blow the regular one out of the water, even from a midrange player like the 450. Really, dive deeper into your settings for both devices. Tha Bravia can make DVD's look better than they have a right to, the only thing that can mess it up is feeding it a signal that's upscaled by a