Bayer Leverkusen matches the same strength with Bayern Munich. You're right, consistency is the only key that will make mediocre club transforming into becoming an elite club. Bayer Leverkusen ranked first this season, they really got some guts to maintain the lead for some weeks. They have one of the best coaches, Xabi Alonso who's not relenting, making sure he knots every area on the pitch. With the present game performance, it will be difficult for any mediocre team to win them, they already know what to expect and they're ready. Xabi Alonso at their peak moment in the present season games.
In history, Bayer Leverkusen does not match the same success like Bayern Munich and in recent seasons, Bayer Leverkusen have not had same strength as Bayern Munich have. They sometimes can create pressure on Bayern Munich in Bundesliga but they even ended latest seasons with lower rankings than Dortmund and with less success than Dortmund.
Bayern Munich are in transition after losing Robert Lewandowski but since this summer, they already got a perfect striker to replace the Polish striker. Harry Kane is expected to help Bayern Munich dominate Bundesliga again. Bayer Leverkusen will be one of victims of Bayern Munich in Bundesliga again like many previous seasons.
Xabi Alonso helped Bayer Leverkusen to improve a lot in the past season but failure of the club in Europa League against AS Roma with Jose Mourinho shows that Xabi still needs more experience as a coach to win big titles. He does not have enough ideas and flexibility to change tactics when his players are struggling in a match.