You are right, Leverkusen was unbeaten last season. Even Munich could not catch up with a fairly large point difference. But Dortmund did not perform well, it was not better than Leipzig and Stuttgart. This season the competition is also tighter. Leverkusen is no longer unbeaten like last season. Some teams are also getting stronger, if Dortmund can not keep up to improve their game, they will be further displaced.
I don’t even see Dortmund among the top teams that will have a chance for the Bundesliga title this season. There performance is not encouraging and will not help in any way to make them a formidable team this season in the Bundesliga. Bayern Leverkusen have surpassed them in performance since last season and as they continue for the fight for the league title, they are the only one that stand the chance to displace Bayern Munich from the top position just like last season. Dortmund performance is getting poorer and until they improve, they won’t be able to achieve anything this season too.
I think Leverkusen is probably still the best opponent for Bayern even though they are still 4 points behind. Well, they are the closest. And the thing is they are playing really well right now. In the last five matches, they have not lost or drawn a single match. But for Bayern, they have lost one and drawn one in the last five matches. So Leverkusen still has the capability of challenging Bayern. Especially if Bayern makes any more mistakes. And even though the difference might seem decent because Bayern Munich is a really good team, but the difference is not that big enough for Leverkusen to actually overcome.
The fight for the Bundesliga trophy this season is still in its early stage and no team will have that full confidence that they will win the title so soon now. A lot can happen in the remaining matches left for them to play Bayern Leverkusen has the highest chances of making it to the top spot if Bayern Munich does not make their form to be consistent. Bayern Leverkusen were able to win the trophy last season and they still have that same possibility of making it happen now since it’s not too late for them.