Bayern Munich didn't stopped to buy players but other team such as Leverkusen lost players frequently and the latest is Granit Xhaka who agree return to England and playing with Sunderland and actually i wonder why Leverkusen owner has decide to sell all of their important players and this factor too makes me doubt Leverkusen can compete with Bayern Munich for next season and for Dortmund too that although so far they buy players to strengthen their squad but so far those players status only averange players and about the domination of Bayern Munich i am sure they can easily to defend their title
I keep telling people that this is the reason why this Bayern Munich have been the most dominant side in this competition over the years, before it was them signing the top names from other clubs in the league it was frowned upon and many thought Bayern Munich have been bullying this teams into actually buying this players but Bayern Munich changed their format and they now go out of the league to actually sign players and yet this teams that are supposed to compete with them are still selling off their best players. Bayer Leverkusen have actually sold three players that are not only their best players but the most senior players, Jonathan Tah, Florian Wirtz, Jeremy Frimpong and now Granit Xhaka.
Bayern Munich on the other hand are adding players to their squad even with this heavy squad that they have, they lost only Musiala to injury and have already gone for his replacement with the like of Luiz Diaz, yet I haven’t seen who Leverkusen will be signing next to fill this void lefts by the departed players. Pressure will now be on the new manager now to deliver which will be hard for him
Let's have a look at Dortmund squad...
They made LB and RB signings this summer and the positions look okay now. When it comes to CB, not so much... Because Schlotterbeck isn't expected to recover from his injury before October.

Niko Kovac should handle the situation depending on Süle's physical condition. You know he gained lots of weight earlier. Lastly, they need an immediate LW signing. Duranville is the only option (
who is injured and not even knowing his return date) after selling Gittens.
I thought this Sule has actually reduce his weight before or did he had more. Seriously they need to add more at that center back, Schlotterbeck was their most reliable center even if he might be back early in the season I don’t think his fitness will make him get into the first team early. For the left wing position I think they are looking at bringing back Jordan Sancho from Manchester United. Seriously aside his wages problem which the player himself needs to understand that he has to reduce I don’t see any problem in his fees. Manchester United can easily take €20m from them. Considering the players last two stint with them there shouldn’t be any problem