Agreed. Do we even know if high end reviewers correct for equal volume level in any published subjective comparisons? They never, ever say in the mags or online reviews. I suspect some do, but some don't, especially those who are uncomfortable with or downright hostile to measurements of any kind. Their ears, I suppose, can adjust for level mismatch. Yeah, right.
As you suggest, the slightly louder of two setups will almost always win the day, preference-wise. I agree that it might be a bogus factor in the preference of DSD over PCM in many "purist" minds, but unfortunately also in many positive reviews of many pieces of audio equipment in comparison to others.