This season Haaland has played really well, but indeed he hasn't been very good this season in terms of fitness. He's been very injury prone this season which makes it difficult for their form this season.
Their performance was erratic as Haaland's condition did not improve.
Now there is new ammunition to replace Halaand who incidentally Haller is also actually quite good in the Eredivisie but indeed it is still quite difficult for them to compete if there is no motivation there.
I agree that apart from Bayern Munich then I think Dortmund is the second team that always has a chance to win the title in the Bundesliga. Haaland played well last season and he has helped the team by scoring important goals, but he has already had his chance to play in the Premier League for Manchester City and that has forced Dortmund to work hard to find a replacement this season. Luckily they have got the expected players, but I don't think the two are the same.
Even if this new Dortmund player has played well this season, I'm sure Dortmund will also find it difficult to keep him from moving to another team. And this is what makes it difficult for Dortmund to win the Bundesliga title because they can't keep their good players every season even though from a business perspective they are champions.