>>33177849 Mallow is rather boring, but she's just a side character and the "big sister" of the group, so I can forgive it, she's not intended to be a "main" girl like Serena or Lillie are, she's just a third a wheel to Ash and Lillie.
Serena though is pure trash. For her first 40 episodes, she did absolutely nothing and had no goals. You forgot she even existed most of the time.