He was playing effectively as a #10 last year because he was the best midfielder they had, and they needed him going forwards. He wasn't the one being asked to retain the ball, he was being asked to get it into his (out of form or inexperienced) front men.
It's not his natural position in my opinion, he's higher up the global midfielder pecking order when he plays in a midfield two or a true midfield three. They played him in that forward role because of his drive and aggression, which is why a while back I compared a couple of his performances, though not his shooting ability, to Gerrard.
When his team's under pressure, he's the one who comes for the pass or chases down. He's not an Ozil, a Rooney or an Oscar 10. He was used as a 10 because Athletic needed someone who could back up a misfiring forward line, by taking some risks from midfield.
I'm not really sure what's happening to him right now. New manager, new instructions and he's not quite found his new role? Who knows maybe he'll be down to our valuation by the end of the season - though, of course we won't want him either if he has a poor season. Dilemmas eh?