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.
Just by looking out the clubs we have already gotten an insight of how next season champions League will look like and the clubs that has a very higher chance of winning and also in the case of Liverpool I would say that they should just focus on the premier League for now because with what they did on this finished season I don't think they will survive on the champions League and also they are still going to go through a little declining in performance as there coach Klopp will no longer be with them next season, so getting use to the new coach will certainly take some time and also Arsenal on the other hand should also focus on the premier League more because that's were they have the higher chance on, however in terms of real Madrid they have already equipped themselves and they are ready for the champions League.
Real Madrid and Manchester City? They are the favorite, the big dogs. Nothing wrong with that. Still, anything may happen in the Champions League. Liverpool, things are changing; a new coach, new enthusiasm. A fresh start can sometimes do wonders. And Arsenal? Though their attention is on the Premier League, never undervalue a club that has something to prove.
Real Madrid, they have an outstanding squad without a question. But that doesnt mean they're invincible. Unexpected events exist in Champions League history. Underdogs can rise and the biggest teams fall. Thats the reason its so exciting.