The reality is that European gravel races, and many American ones too, favor the same sort of rider that does well in moderate to difficult, though not necessarily technical, road classics. The best riders with these attributes are in the road peloton. Bring them to Unbound and they would win too. I don't think the technical skills of an XC specialist overcome the better endurance of a road rider unless the course is essentially a MTB track.
Don't get me wrong: I love gravel and challenging tracks. I'll be riding some rocky logging roads today. But that is not where big time gravel racing is heading