It will take time for Ten Hag to make changes at Leverkusen because after all the departure of Xabi Alonso has made this team have to go through adjustments. The target next season to compete for the title but it will be difficult to achieve if Leverkusen does not strengthen the team with the swelling of several important players. Everyone associates Ten Hag's failure at Manchester United and maybe many people are pessimistic that Leverkusen under Ten Hag's coaching can be much more successful. Anything can happen but we need to give him time and trust him because who knows he could repeat the success he had at Ajax.
A team like Bayern Leverkusen that have tasted success recently will want to continue to taste it. They failed to win the Bundesliga title last season and lost to Bayern Munich who reclaimed the title from them after they won it from them last season.
I think it will be difficult for Bayer Leverkusen to challenge for the Bundesliga title next season because Bayern Munich is building up a squad that can win the Bundesliga title in the next 5 years, which will make it difficult for Bayer Leverkusen to win the Bundesliga title. Secondly, Bayer Leverkusen sold some of their best players to other clubs, which will make their performance decline, and that will even make it more difficult for Bayer Leverkusen to rival Bayern Munich for the Bundesliga title next season.
I think it's too early for you to come to conclusions as to why you think Bayern Munich will possibly remain champions and dominate the league for another five years, Bayern Munich got better than Leverkusen last season and they are building up the team again with the players they are attracting to the club but the transfer market is still available and the current coach of Bayer Leverkusen still has time to shop for new players that will help the team to get better so that they can still challenge Bayern Munich next season and more season to come.