Even though, I may have no experience to often compensate for my answer, but what I consider skill is when someone is consistently getting better under different circumstances. Someone who can keep trying even if they miss a fruit or a droplet. The ability to keep going even if they are in the boundary of failing. That right there is what makes a person pro in my opinion. Also, it has nothing to do with the sheer fact that he/she can play insane++ maps. I feel that I could consider someone skilled at Catch the Beat when they complete a map on any difficulty. It's all about growth, baby!