It's not a matter of Erling Haaland moving to any other club which causes the alarm in people's minds. It's about Erling Haaland moving to Bayern Munich which is absolutely dumb. 
I don't know why would Dortmund make that decision. I think obviously Dortmund is not going to make that decision unless they are on drugs or something!!
At a time when people are thinking Bundesliga to be a more competitive league and having more teams to compete against Bayern Munich, it does not make any sense to allow Bayern Munich to be stronger. I agree that it is really boring for the fans to watch Bayern Munich win the title again and again.
It is what Dortmund would eventually do, they would eventually let go of Erling Haaland to make a huge profit, Dortmund is already doing this kind of cycle whether you like it or not they would eventually sell all their good players to clubs like Bayern Munich that can really afford them, and Bayern Munich is a club that can surely afford their number 1 player, so the possibility for Erling Haaland to be on Bayern Munich would have a higher possibility, and now that Erling Haaland rejects Man City offer said by rumors, I don't know why would Dortmund make that decision. I think obviously Dortmund is not going to make that decision unless they are on drugs or something!!
At a time when people are thinking Bundesliga to be a more competitive league and having more teams to compete against Bayern Munich, it does not make any sense to allow Bayern Munich to be stronger. I agree that it is really boring for the fans to watch Bayern Munich win the title again and again.
And yeah it is not really balanced for a team to have all good players but Bayern Munich is a club that can afford to buy good players that they can afford, but there is a possibility if they bought Erling Haaland they could even Let go of Robert Lewandowski,
You are right. Dortmund is called the club to grow young players and sell them for a huge price. Dembele, Sancho, Lewandowski are just a few examples. Haaland will be the same. He is already an exciting one in the transfer market for RMA and City. Since he rejected City, Bayern might also be a good place. What I think will happen is, Haaland will go to RMA, and if not RMA, he'll join Bayern and Lewandowski will go to either City or RMA.