I think we're very much approaching this from the POV of the player, and what they regard as their best position - from that perspective then, yeah, you'd have to look at it and say that we're not really adding much to their games, or coaching any new abilities into them.

However, I'm not sure this is how Wenger looks at it - I think he sees it from a more functional, 'play to your strengths' perspective, and will try to find a player a role in the side based on what they're best at (which isn't always what the player thinks they're best at, or where they thought they'd be playing)? Coquelin's probably the most recent example, albeit a fairly subtle one - by all accounts, he was trying to play beyond his ability as a central midfielder, and was losing his way by trying to add too much attacking play to his game until Wenger took him to one side and told him to just focus on the defensive side of the job. Thankfully he took it on board, and he's now focussing on doing one job to a world class standard before he starts pissing around with anything else.

Generally speaking, I think the success stories are the players who are humble and honest enough to accept our assessment (or reassessment) of their abilities, and who embrace the role we give them. And the ones who fail to make any significant impact are the ones who never quite find a place in the side: either they never fully accept the job that we give them, and their ego (or entourage!) tell them that they're destined for other things (sadly all too common with a lot of these teenage millionaires); or they simply don't have any one skill or attribute that makes them anything special, and we never really find a specific job for them beyond being a bit of a utility man (there's still a good career to be had in that, but it probably won't be a glamorous one)?