Would you say Bayern was bad last season when they won the Bundesliga? I'm guessing your answer would probably be no, but the fact is, this season they've scored 1 point more than in the last one. They also got through to the Champion's League semi-final and fought a good fight against the winner, Real Madrid.
They failed to achieve their goal in the league, but calling that a "really bad" season is a bit ignorant.
Bayer Leverkusen has won the league undefeated, established a new record of games without a loss, and were very close to setting a new record of most points in the league.
There's just no pleasing you, it seems.
Bayer Leverkusen in the other hand won the German Bundesliga in the most successful style ever known in the history of the league because they finished an entire season without conceding a defeat. Next season, it's also impossible for them to achieve everything they achieved this season because of how careful the teams that'll face them will be.
It is really a bad season for Bayern Munich last season based on who they are. It has been long that Bayern Munich missed the title and this should the a warning for them that other clubs are building their team to be very strong in order to win the title because they are not the only club in Germany.