I explicitly asked for the colour gamut and bit-depth coming from the device, not the Dolby Vision mode on your TV.
- To support more formats(Dolby Vision profile 7, TrueHD, DTS HDMA),
- have more features (like upscaling on the shield),
- more ports and connectivity
- smoother interface.
- Gaming (apple arcade, simulators).
The only things that impact PQ is your TV screen and the data in the stream.
It's definitely worth it to get an Apple TV 4k over cheaper sticks as it offers a lot wider feature set. However, PQ is not a reason to choose. This is why no reputed hifi forum even discusses the PQ of a streamer in the review.
If the PQ is different between two streamers, that means one of three things:
- One of the streamers doesn't fully support the format (say one streamer is DV while other only does HDR, or one is 4k while other is 1080p).
- Something wrong with the settings on your TV/HDMI/streamer.
- A bug in the app of one streamer.
A digital stream is just ones and zeroes. Streamers send that ones and zeroes to your TV. Just like digital audio, there's no point in discussing PQ until the conversion from digital to analog happens.
Cheap Chinese streamers don't even support as many formats as the firestick. The Mi Box S doesn't support Dolby Vision for example.