Leverkusen started the season badly so that they lost several points, but now the squad coached by Xabi Alanso seems to have found their identity again, we can see as you have said, the squad coached by Xabi Alanso has always won in the last 8 matches. Leverkusen's current revival of course makes Bayern Munich no longer feel safe at the top of the standings because they are only four points behind, with the season still long of course the opportunity to overtake Bayern Munich is still wide open.
Leverkusen never started the season badly just that they dropped a bit in performance but they picked up after some games and since then they have been in a good form. They have only lost one match this season alongside Bayern Munich which is to show that they were never in a bad form since the season started. Xabi Alonso has already built a strong squad since last season so they are just continuing from their last season performances and experience and it seems they will become the strongest rivals against Munich since Borussia Dortmund that used to be Bayern Munich's strongest rivals have not been stable for quite some seasons. Bayern Munich will surely feel threatened by Bayern Leverkusen's consistency but the problem Leverkusen will face is Bayern Munich's goal scoring streak, like they have huge goal difference and they have also conceded the least goals so far.
However, even though they are currently only four points behind, Leverkusen should not be happy yet because in the next match they will face a tough match which is having to travel to Dortmund while Bayern Munich will travel to Borussia Mönchengladbach. Leverkusen and Bayern Munich have the potential to lose points in this match if they make a small mistake because of course the host will also fight to get points in order to improve the standings. So it is very true as you said, for now there is no team that dominates the Bundesliga because both Leverkusen and Bayern Munich have the same opportunity.
I don't think Borussia Dortmund will be hard for Bayern Leverkusen to win because even though their form is not too bad but their energy can not match up with that of Leverkusen. Perhaps, since Leverkusen is aiming to cover the gap between them and Bayern Munich they will play Dortmund with all their strength in order to win. Bayern match against Monchengladbach will be an easy game for Munich, so they will still continue at the top till they meet strong opponents like Leipzig or Eintracht Frankfurt. Bayern Munich and Bayern Leverkusen may seem like they have equal strength but Bayern may not give Leverkusen same opportunity they gave them last season.