I wouldn't define skill purely by practical things such as landing on this planet, or by building a ship this big in orbit. Sure, it's impressive, but that's merely a manifestation of skill; not the skill itself. To me, a skilled player is a player who knows how the game works and who can use that knowledge to complete whatever tasks they want done. They know what they're doing, they know what they're doing wrong, and if they do something wrong they know how to not do it again. A bit vague, perhaps, but that's the most general thing I could come up with. After all, having yet to land on and return from Tylo doesn't prove you're unskilled. It just proves that you have yet to do it.