I agree, we want to match Windows behavior where we can, but I don't think that change is within the scope of this MR.
Well the scope of the MR could be to add support for the P010 format, which will be useful to implement that AV1 decoder. IMO you could drop the one I420_10LE to P010 mapping hunk for now (or replace it with a mapping to GST_VIDEO_FORMAT_P010_10LE).