For mine, if he can't make it in the Eredivisie, he will struggle anywhere in Europe that is at a good level. The Eredivisie is basically tailor made for smaller, trickier, younger players to flourish.
I think his injury when he first went to Germany really hampered him, and I also think that he perhaps is just simply too small to really succeed consistently. Ryan Thomas is considered small too, but he's a beast compared to Marco. You need to be exceptionally good to overcome that limitation, and I don't think Marco is quite at that level.
Kosta has found his level in the A-League, and I think Rojas level is similar. Rojas needs consistent game time and he hasn't got it since the Vuc.