Since being coached by Xabi Alonso, Leverkusen has transformed into a club that needs to be reckoned with by every opponent, especially in the Bundesliga, and Leverkusen's potential to defend the Bundesliga title this season is still wide open, especially since the squad has not changed much from last season's squad. Plus Bayern Munich and Dortmund will start to adapt a lot because both teams are coached by new coaches. But it is true as you said, the Champions League competition will be very different, this is a competitive league and even the atmosphere will feel different so it will not be easy for Leverkusen.
This is the test that Xabi must conquer at this time because a tough test awaits them this season, especially with the expectations given by most people to make the Bundesliga interesting, of course this is a heavy burden for Xabi and Leverkusen, especially for the current season with the status of defending champion, their goal is definitely clear, namely maintaining the existing trophy not as a trophy chaser which they always did before when Bayern became a champion subscription.
I expect this from the bundesliga because even though Bayern are currently still the favorites to win but it cannot be denied that the presence of Leverkusen at this time will certainly add to the situation to be more interesting in the bundesliga because there is new hope in competition after so long we are too saturated with Bayern who always occupy the first place and this time there is competition made by Leverkusen which makes the bundesliga more interesting.