Last season was indeed a fantastic season for Xabi Alonso and his team they did so well in all competitions winning the league title without recording a single defeat, the league cup and finishing 2nd in the Europa League finals against Atlanta shows how strong the team was last season. The team was in another level last season because they had some many incredible comeback which no one expected them to have they were so lucky and strong even the biggest team in the league Bayern Munich couldn't catch up with them till the end of the season.
All these achievements happened to Leverkusen last season, but it is very unlikely that Leverkusen will repeat this again next season, although it is not impossible for Leverkusen to achieve it again with Xabi Alonso. Moreover, next season Bayer Munich itself will be handled by a new coach who generally will definitely need a little time in terms of adaptation and other things. So Leverkusen could put this to good use again in order to repeat what they achieved last season in the Bundesliga by never losing until the end of the season.