kschuster, here's the short answer
I'd say his poor performance was mainly due to his
lack of adaptation to your team combined with a lack of experience in general. Unfortunately adaptation rate and experience gain rate are both hidden stats, so there is no way to tell just how long it may take for him to adapt. Usually it takes anywhere from around a month to around 6 months from purchase to full adaptation. Experience gain rates generally vary between 1 star/30 games to 1 star/60 games or so.
The player is by no means "world class" but his skills are around average or even slightly above average for your league. He should do much better once he has fully adapted to your team and more so as he improves his skills as he reaches his LA.
Moving forward, I'd suggest you focus on training off the ball, stamina, and speed (acceleration and pace) if you like to use the "more roaming" tactic, although you should check those links lordaust posted if you want to use different tactics. Use him at least 30 minutes in as many games as possible to speed his adaptation and experience gain!
Good luck