I can say that I do not find the possibility of Leverkusen to beat Bayern in the league too realistic. In my opinion, the only team that can beat Bayern would be Borussia Dortmund. They also lost Haaland. Good players to fill their place should be transferred. Dortmund is a team with very good players. They could be a little better.
If you look realistically, then no team has a chance to get around Bayern. Usually an "average" or top 2 team has a chance to beat the top 1 when the top 1 gets into a generational change, then one or two seasons of the top 1 is weakened. But in Bavaria, this process is put on stream and they are gradually replacing players all the time (the situation with Lewandowski illustrates this well) - they even find replacements for the stars. In order for Dortmund to become at the level of Bavaria, they need not only to make a profit and be satisfied, but to invest this profit in the players and the club, in fact, Dortmund's income is only two times lower than Bayern's, but the results are incomparably worse.