I don't think there's anything wrong with Dortmund's first-team squad. the rotation of players in the team when playing matches that have a short time lag may be still less balanced. the main players on the team with the players who are the reserves still lack the same experience. because sometimes we see Dortmund playing very well, but also sometimes mediocre.
Dortmund don't have to beat other clubs but also have to beat Bayern in long run, in a whole season. And with their unstability, it is impossible mission. Haaland likely has his last moments in Dortmund and with his departure, Dortmund will lose about 50% of their strength so next season, Bayern will dominate Bundesliga again.
Dortmund only can fight at their best and dream about Bundesliga title in this season. If they can not touch it, they will have to wait for next 2 to 3 seasons, if they can get another good striker as replacement for Haaland.