I agree with you that Bayern Leverkusen will be stronger next season. Bayern Leverkusen's performance this season is not luck; if not, they wouldn't have displayed the same performance in the Europa League competition. Xabi Alonso knows the tactics he has deployed at Bayern Leverkusen that have made them successful this season in all competitions. Bayern Leverkusen has made their fans happy by winning this season's Bundesliga title. They are waiting to play the DFB Pokal Cup finals and the Europa League finals, and they are unbeaten in 50 matches played this season.
Bayern Leverkusen took their football to another dimension this season and they have achieved the fruit of their labour (bundesliga) even if they don't succeed to add another trophy to their name this season why is impossible because if they don't succeed in winning the two finals awaiting them ( DFB Pokal Cup and the Europa league finals) they must win at least one among them because with the consistency they have shown even till this ending period of the season have shown that Xabi Alonso really came prepared for Leverkusen this season and who would have believed that Xabi Alonso can lead Bayern Leverkusen to their first ever bundesliga trophy in the club's history.
Since Xabi Alonso will still continue with his managerial role for the club next season, Leverkusen will soon become stronger and dominate German bundesliga alongside their counterparts Borussia Dortmund and Bayern Munich so will should be expecting huge competition in the Bundesliga from next season even though Bayern Leverkusen may not have an easy ground next season but they will make the league become more lively.