I agree that Leverkusen was always strong and they were even racing at the top of the table with Bayern Munich and Dortmund but they are much stronger this season with their coach Xabi Alonso. They had a good performance in the last season but Leverkusen didn't have many good players and the team tried to help Xabi by hiring the players he needed, that is why they are in the top side of the Bundesliga because Xabi Alonso was a great advantage for them.
Xabi Alonso success in managing Laverkusen this season has been phenomenal, going seven games unbeaten and topping the Bundesliga standings. I see Bayern Munchen dominance starting to be threatened even though they have better squad depth than Laverkusen, but in terms of strength I think they are quite balanced. The draw in their second meeting in the fourth week is proof of Laverkusen strength this season, just waiting to see how Laverkusen strength will be when facing Dortmund.
The Bundesliga standings have become more competitive with Laverkusen consistency in winning points, if this continues their chances of winning a trophy at the end of the season are wide open. Thus, Munchen decade-long dominance was broken by their own former midfielder Xabi Alonso. Dortmund almost did it last season, finishing on the same points but falling behind in the goal statistics.