HI10P is heavy heavy heavy to decode. Any little extra performance helps. If you force a color space conversion to yv12 (or something else non 16bit) you, not only, loose quality, you also likely make it unplayable on some devices.

And as you say, there is no point in using DXVA for hi10p. We should avoid options that users have to toggle on and off based on what file they are playing.

With my proposed change: DXVA would be selected for all non hi10p formats and non DXVA renderer would be used for the other. Ie keeping pretty much best of both worlds.