I assume the reason some people underestimate Leverkusen is that they believe Ten Hag still needs time to adapt and that they are no longer the same team inherited from Xabi Alonso. But even though Leverkusen is in a period of transition, they still have more advantages in many aspects compared to Hoffenheim. Overall, I think Leverkusen is still considered one of the trophy contenders this season.
I am also considering the changes the team undergone; they lost some key players and didn’t sign perfect replacement for them yet, which will surely affect their performance in the Bundesliga this season but that shouldn’t be an excuse for them to perform poor this season because Ten Hag is a good coach and can do his best to improve the team this season.
Leverkusen remains among the title contenders because they were among the top three teams in the Bundesliga in the past two seasons, and since we didn’t see any improvement from Dortmund and any other team; only Bayern Munich is rated ahead of them in the last two season, but since they signed Ten Hag, people are not valuing the team anymore maybe because of his past performance in Manchester United.