Bosz biggest mistake is forcing Weigl to play a higher role in his shitty 4-3-3. Instead of stay deep and dictating the play, Weigl is forced to play much much higher, partake in high line pressing and making runs because Bosz love his fecking high line that he has to push Weigl forward. He's turning Weigl from one of the most promising (maybe even one of the best) deep-lying playmaker in the world to a shitty, useless CM.
Weigl and Raphael Guerreiro are propably the only 2 WC players of Dortmund. Yet he's destroying Weigl, forcing Guerreiro to play somewhere else because of the Schmelzer - one of the most useless and limited LB that i've ever seen.