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.
RB Leipzig win is impressive as this is now good opportunity for the other teams to have better performance and results against them while things are surely not easy for them because now they are also having challenging time in Champions League we will have some pressure on them and Xabi Alonso.
Last season we have Bayern Munich troubling and then Borussia Dortmund was also not performing as they needed, but now we have few good improvements like Borussia Dortmund is back on good and Bayern Munich's start is also good, so things are surely interesting for all top teams I am expecting surprise from the RB Leipzig with things will be good between them for staying into top four as it's never been easy for anyone.
From here now all is wide open for the top teams to deliver and have their best because with this start all are looking on same level of quality.