Yes the pacing is absolutely terrible. It’s the same issue I have with One Piece and Naruto. I find a number of long-running anime run into this issue. Toriko was another one that fell apart (towards the end).

To be fair, Shonen anime is aimed at teenagers and young adults. I think you are unintentionally perpetuating a common misconception about anime when you say it’s for children. I think it’s one of the reasons why so many Americans automatically think cartoons and anime are the exact same when anime is far more nuanced than that.