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.
Adding Mbappe to an already tough team with a lot of potential to be consistent and continue to win trophies is a big gamble of no mistake, I mean they’ve bet well on this because it’ll most likely result into bigger success for the team. Real Madrid this point are still the best candidate for the trophy as they’ve strengthen their squad and also have a very big god track record on this competition. You don’t expect nothing but success from this team when they play. With a lot of changes in the managers of most of the top teams in Europe, one can see that the next season’s champions league won’t going to be as easy one. All this managers will want to try their best to improve their team in order to keep their jobs in the various teams they are doing their management under.