Not that I disagree entirely with you, but didn't you write somewhere (correct me if I'm wrong) that players take a long time - often as much as a season or so - adapting to the PL? Combined with the fact that Sahin has barely played competetive football for a year now, it doesn't sound to me like a player that'll send a team straight to the top of the PL.
It usually does take foreign players a season or more to adapt to the Premier League and show their best. Only occasionally are there a handful of foreign players that from day 1 look like they were born playing in the Premier League. I think Sahin is good enough to be one of those players.