I was looking for a post about the Skill rating and what it does. After reading the post and looking at what I could look at am I wrong in thinking:

The Skill rating could be described as a modifier to a players abilities. It is the players abilities that will drive how he does, but a higher position skill rating means the player is able to use those abilities better.

That's how interpret it and if I'm not wrong it can increase with playing time, so for me it's almost like a 'positional familiarity' modifier.

The "Skill" rating on some screens is just the current Skill rating for the player at their current assigned position. To see all of their positional skills you have to look at the player form. But I think you're on the right track.