You are good at PvP'ing when PvP'ing? What do you think you're good at when PvE'ing? The only difference is that one is competitive and the other collaborative, but they're ultimately about the same thing.
What keeps you coming back for more? Wouldn't you rather a fair 1v1 match with rules? The point is, people stick at these kinds of thing because they think they are being 'good' at something and want to impress others. What exactly are you 'good' at when you are PvP'ing?
Knowing game mechanics and gear, anticipating other player's moves and countering them IS skill. Comparing it to playing musical instrument is meaningless. When you are fighting another player you are using your skill to win and the other player is using his to win, it doesn't matter whether you have a hundred options or two, it's still about building a character with the right set of options, as few weaknesses possible, and anticipating the other player's move so you can counter it, or you lose, that's 100% skill based, moreso than PvE where auto-completion is half-expected. PvP is the hardest thing to be good at in DDO, it's hard because you're up against something no AI can ever compete with: someone who can outsmart you.
Don't make me laugh these games are about knowing the game mechanics and gear, there is very little skill beyond learning and being able to remember that knowledge. There is very little mental or manual dexterity involved beyond pressing a few keys and pushing a mouse. Other games like RTS and FPS are much harder to master, but still pretty basic as far as any sort of dexterity is involved, but even those pale in comparison to say, playing a musical instrument.