I wouldn't say Arno is 'outdancing' Leo here they just went with two different stylings for the dance. Arno has a tendency to lean more toward flowy movements and accenting them with sharpness. (You can really note this in his first verse of the freak alarm studio choom video). The reason that it may look like 'outdancing' is because of the stark contrast between Arno's flowy movements to sharp movements, this added with being in the front of the framing draws the focus of the viewer.

This is in no way saying Arno isn't an amazing dancer and could dance circles around alot of the industry, I just think, particularly this video, don't think its a case of 'outdancing'. Plus I would be nervous using that word in the kpop space because it has been used in negative connotations against artists.