After a few successful seasons, club like Leipzig will be challenged by big clubs in transfer seasons. Their players after dedicate a few seasons without titles, will want to leave and find a new higher highs for their career.
Because of attraction from transfer deal, financial income and pressure from their star players, they will lose their best players. It will be a start of their troubles.
In Bundesliga, Leipzig already have more competitors like you said, Mainz, Wolfsburg and Freiburg. They will struggle with those clubs to complete this season with a good position and a spot in Champions League.
That is life, and it goes to show's that Leipzig is not the same anymore, with that 5 departures of their good goalscorer it's like Leipzig has been disabled in both offensive and defensive with Dayot Upamecano now in Bayern Munich, Marcel Sabitzer now on Bayern, Hannes Wolf now with Gladbach, Lazar Samardzic, Alexander Sörloth, Ibrahima Konate, Ademola Lookman, Hee-chan Hwang, Caden Clark, and Fabrice Hartmann was Leipzig doesn't able to pull that great plays last season, even e though there are players that have been added to the rooster I think this is not enough and Leipzig is not really functioning very well.
^ I don't think Bayern will struggle that much if a player or two get injured in my opinion. Because you know, last season they were somewhat heavily dependent on Lewandowski and his goals. But this season they have a very well team game. Seems like almost everyone is scoring and assisting. Yes if Lewa is injured their scoring chances will decrease a bit, but not so much that they will start losing.
Yes, I think you are right, last season they are very heavily dependent on Lewandowski alone, but right now Serge Gnabry, Thomas Muller, Joshua Kimmich, and Leroy Sane is pretty much doing great and upped their gameplay, and with the addition of players like Dayot Upamecano and Marcel Sabitzer from RB Leipzig, Omar Richards from Reading Football Club, Sven Ulreich from Hamburg, both a free transfer, I think that Bayern is fully packed with great players, that is why even without Lewandowski on the field Bayern can surely hold on its own.
In my opinion, Leipzig's performance has decreased so much this year, because they were abandoned by Julian Nagelsmann. I see the strategy
used by Nagelsmann is very effective, making Leipzig good in attack and strong in defense. What hurts is Nagelsmann decided to move to Bayern
this season which is a rival to Leipzig, finally this season Leipzig played at a very much different level.
Moreover, the players who have brought in Leipzig this season have not contributed, and I think that even if Leipzig want to sign players of
the same level as Lewandowski or Haaland, it's impossible. Besides Leipzig's finances are not so strong, it is very difficult to convince star players
to play in Leipzig. If this season Leipzig managed to enter the top 5, it would be a pretty good achievement. because with the quality of coaches
and players that Leipzig currently has, it is very difficult to compete with big teams.
Yes! that is another assumption why Leipzig is so poor with their performance, and right now Julian Nagelsmann is on Bayern Munich right now and right now I have seen in the news that Nagelsmann right now is tested positive to Covid, but I think even without Nagelsmann Bayern can surely hold on, Leipzig in contrary can kiss the championship goodbye for this season if they don't get their acts together.