I'm sure there are people who are good at sparring that aren't good at GSing, and it's probably because they don't enjoy it or care to invest the time to get good at it. Jack, Kevin, etc. I feel like if you're good at sparring then you're good at everything required to be good at Graal in general: understanding hit detection, comfortable with movement, you know how to work with blink, you understand the forms of lag, etc.

The best sparrers could be the best at events, towering, stupid stuff like catching bugs, etc. It's all the same skillset. Some people have the patience to tolerate GSing and others don't, that's all I really think it is.