That is right, Grosskreutz has always been just a reserve player. The only reason he is still in the team is because Perisic left during the winter transfer period and I guess Borrussia didn't want to introduce too many new faces in the middle of the season, so they just relied on Grosskreutz. Also, he's like one of the most hated players in all Germany, so getting rid of him would be quite convenient for Dortmund.