Bayan Munich can win against Leverkusen but it is wrong to think that Bayan Munich will win every match against the teams you consider easy opponents. We often notice that in important matches big teams are defeated by relatively smaller teams or do not get full points in those matches. Bayern Munich should not plan all the matches at once, the match they play is important for them and they have to win that match. Leverkusen went undefeated last season to secure the title, but that doesn't mean they are stronger than Bayern Munich.
Leverkusen has looked a little different after winning the Bundesliga last season with an unbeaten record, but this season it is no longer the case because Leverkusen has lost when facing Leipzig in the second match at the beginning of this season. But in terms of strength, Leverkusen must still be considered a dangerous opponent by any team in the Bundesliga because Bayern Munich must not underestimate an opponent like Leverkusen, especially since Bayern Munich is also being led by a new coach this season.
Leverkusen was a name of terror for all teams in the Bundesliga last season. No one expected Leverkusen to perform so well all of a sudden. Another big reason why Leverkusen did so well last season was that the big teams didn't have much of a plan for this team. However, with the performance of this team last season, each team planned separately against Leverkusen, which resulted in this team losing one match at the beginning of the season.
I said last season that Leverkusen won't be able to perform as well as they are doing in the Bundesliga this season, and I've been putting Bayan Munich ahead ever since. But I must agree with what you said, any big team can be beaten by Leverkusen so every big team has to be careful and make no mistakes especially Bayern Munich if they want to win the Bundesliga title next season.