I have an LG UHD TV model from 2020 running webOS and I haven't noticed any performance issues either with Prime Video, UHD, HDR or otherwise. I use Bluetooth speakers/earphones for audio. The sound is almost perfectly synced with the video in Prime while there is a noticeably annoying delay in the Netflix app on the same TV.
To be clear, my beef is with the browsing UI, not the playback. The playback on all these devices is handled by dedicated hardware. It's not like Amazon's app is decoding videos in a WASM VM.
Well, X-Ray is a feature in the Prime app that I like and use quite often and is very snappy. Since it's part of the UI overlay, I think it's handled by the WASM module (probably with local caching)
and not by the dedicated video-decoding hardware in the TV.
I agree that the browsing UI can sometimes take an extra second or two to refresh which I don't find to be a dealbreaker since it's the video/audio playback that I care about the most.
