According to Wikipedia he scored 20 in 55 games (including the 3 from yesterday), but score only 3 in 18 last season. Doesn't seems like a reliable goalscorer to me.
Well then stop looking at wikipedia.
He literally missed the first half of last season due to injury and only managed to play in 1,056 minutes the whole campaign, which is about the equivalent to just under 12 games.
3 goals and 1 assist in just under 12 games of an injury ravaged season in the Bundesliga, when coming off the back of a 14 goal and 3 assist season isn't bad at all at the age of 23.