The consensus here seems to always be leave in SDR and use match content, but I’ve had no issues with leaving Dolby Vision on all the time. SDR content like youtube and TV shows that were never mastered in HDR look 100% fine to me. Part of the Dolby Vision spec is that it forces your TV into it’s most color accurate settings so why wouldn’t I want that as well? Using an LG C2 by the way.
Two reasons.
A). A surprising amount of SDR apps do not flag their video output correctly when the Apple TV UI is set to HDR/DV, and therefore, either they do not switch dynamic range properly, or they do not map out correctly their video/color levels within an HDR signal/container.
B). Perhaps more importantly, the tvOS interface is not, I repeat, is not, natively rendered in DV. Therefore, when you set the default Apple TV video output to DV, a conversion from SDR video levels happens, which affects both color and accuracy.
In sum, set your Apple TV to 4K SDR 60hz, RGB High (to avoid the green tint bug with SDR content when set to the default YCBCR), and enable both range and frame rate matching. That’s it.