That is very good way to look at next season in Bundesliga. It is likely that Dortmund will finish in top four but most interesting part will be fight for second place. You are right that there is big difference in strength between Bayern Munich and rest of league. This could give Dortmund chance to finish second if they have strong season. However as you mentioned teams like Leipzig and others are serious competitors. Race for top spots below Bayern is going to be very tough and those teams will definitely be challenge for both Dortmund and Bayern next season.
I will not be surprised if eventually Bayern Munich looses out on this seasons Bundesliga title but with leipzig, and Dortmund I do not have a particular, they both frequent the top four positions on the table often, it will be almost like a norm if it happens that both of them eventually finishes top four or even either of them but with the title Leverkusen even looks more viable than this other two for the title.
Bayern Munich will eventually lift next season league title they are very inform, no team can stop them right now in Bundesliga, Leipzig, Borussia Dortmund and Bayern Leverkusen cannot stop Bayern Munich from lifting next season League trophy, Bayern Leverkusen he still having a problem I really don't know if ten Hag can carry the team the way the former coach did even if he can since he's still coming newly he has to adopt into the team very well before anything can happen, so for now Bayern Leverkusen is out of the way they cannot lift next season Bundesliga trophy, as soon as the League starts I will bet on Bayern Munich to lift the league title at the end of the season they have good players and they are very determined in making sure that they will lift the league trophy again.
They can even lift champions League trophy next season if they put more effort they have good player like Harry Kane and others, but for next season Bundesliga trophy they will lift it next season I trust them.