I agree with you that Champions League will be more competitive next season. The Leverkusen team is very strong despite not having many star players. On the other hand, Manchester City will try to strengthen their squad next season. Reigning champions Real Madrid have already managed to strengthen their squad by adding Mbappe to the squad.
Arsenal have played very well in the Premier League this season. However, there were several weaknesses within their team. Arsenal coach Arteta will try to strengthen the team this season. Moreover, Liverpool's new coach will also be looking to strengthen his squad.
The fact that next season will be hot and probably more fierce than this season because of the way many clubs are restrategizing today and are still working to correct their wrongs against next season. Some of the prospective clubs this next season include the defending champions themselves which is Real Madrid, and they have gone ahead to take more big plans which includes the coming of Kylian Mbappé to the club. I will mention Dortmund because if they can try and add more efforts, they can reach the final for the second.