Felix Nmecha’s defensive output and ball progression
Looking past Nmecha’s attacking output, you see his tackle and interception numbers are higher than Borussia Dortmund’s main central attackers but lower than both midfielders, despite his team having considerably less possession (the equivalent of 146 minutes less over his ~1800 minutes played). This makes his numbers look a lot worse. Also Edson Álvarez, while a more defensive midfielder, plays for an Ajax side that has been known to dominate possession in the Eredivisie, still has more defensive actions per 90 than Nmecha.
When looking at the Borussia Dortmund squad as a whole, having swapped Raphael Guerrero for Ramy Bensabaini and multiple young attackers (that should in theory get better); the main traits lost by the squad are in ball retention and ball progression.
Both Guerrero and Bellingham excel at passing and carrying the ball up the pitch. The question for all players when joining a ball dominant team is will more time on the ball expose their flaws in possession or emphasize their strengths?
Nmecha ranks in the bottom 15% of both pass completion percentage and passes attempted by all midfielders. Nmecha additionally has the worst short passing game in the comparison used, which means that as he transitions to a ball dominant side, he would likely struggle to keep up with more talented teammates. By joining BVB, Nmecha would be asked to do a lot more of what he has struggled with in the past.