Sony A7SIII's files tank performance even on highest end rigs when trying to edit some files like 4K 120fps. I need to setup proxies or transcode for usable timeline editing.
I never assumed AMD has better encoders. If they had support for this one specific use case, it would be worthwhile for me to forgo Nvidia's cards in this specific case.
Have you seen this chart?
https://developer.nvidia.com/video-encode-and-decode-gpu-support-matrix-new
It not unusual to need to transcode for better performance.
What editing software are you using? Some tools/versions do not support GPU decode for playback. For example, the free version of DaVinci Resolve does not support hardware accelerated playback, where as the paid version does.