Bellingham was Borussia Dortmund's biggest weapon. The same situation was true for Haaland last year. The team got a little worse after Haaland left. After Bellingham left, Dortmund got worse. Dortmund is a team that is adept at recruiting young and talented players. They may be bad this year, but they can make up for that deficiency soon. The observer team is very good.
I wouldn't at all compare Bellingham with Haaland and also not confuse the recent success as a goal scorer with Bellingham being a full mode striker. It could be and it will still take some time to see whether Bellingham can keep going and scoring. But the biggest weapon Dortmund had was Haaland for a while and Bellingham was very good, but he never as decisive as he has now been for Real Madrid. It doesn't happen very often that a player decides a few games in a row in the last few minutes.
For Dortmund Bellingham scored a goal around every 8 games. For Real Madrid he scored 4 goals in 3 games. To me this is most likely more of an outlier than the expected standard.