When I say I want to get "good" at something, it has meaning. For example "I want to get good at playing jazz." or "I want to be a good cook." It doesn't mean "great" it means competent, able to do the task with some skill. It does have meaning. A good jazz pianist can play in more than one key, and not only at slow tempos. A good cook can do more than "enjoy" their packaged food they heated up.
As to skiing to me being a good skier means being able to be in control in a variety of conditions and pitches. To have a minimum amount of panic or fear, and be able to ski not only on groomers, but in ungroomed and steep terrain.
Having fun at something doesn't mean you're good at it. It means you're having a good time - which is great, don't get me wrong. But if you get scared and can't control your speed without snow-plowing and excessive skidding when the terrain gets a little challenging, you're not a good skier.