When I looked up the stats i'am quite shocked. At Hoffenheim he scored 16 goals. He played 33 times last season.
This condition means he is able to play regularly at Hpffenheim. In addition, at the age of 21, Dortmund invested in promising players.
Yes he has for sure some awesome stats for the last season and years for his age of 21.
I guess he wanted to make the next step to grow and also wanted to play on a higher Level by moving to Dortmund even there are a lot of other good players.
What is certain is that now the main path is open by joining Dortmund and if he stays at Hoffenheim maybe no club will see him.
Well, muscle mass is very important and if he knows that is the main capital that he must have before being excited with adrenaline as an experienced striker.
I agree fully that he would be remained In Hoffenheim that maybe he would be unknowen for bigger Teams.
Also about his fitness and the muscle mass they will work on that in Dortmund.