>>16351079Misty has displayed mastery (defined as a deep understanding) of Water-type Pokémon. That means she's well on her way to being a Water Pokémon Master, like her goal. Misty was always the "black sheep" of her family and she was motivated by the desire to break free of her sisters' shadows.
May wanted to travel, and had no interest in Pokémon or Pokémon training because she felt resentful of being shoehorned into a goal just because her father was a great Gym Leader. This alone set her up as an interesting character.
Dawn knew what she wanted to do from the start. We were never forced to sit through her being wishy-washy or clueless. By the time she had her "identity crisis" we were already invested in her story. That's why it's called character development. It should only happen once you already care about the character.
Iris has displayed mastery (defined as a deep understanding) of Dragon-type Pokémon. That means she's well on her way to being a Dragon Pokémon Master, like her goal. Iris struggled to fit in with society and her clear-cut goal from the beginning was to evolve Axew into Haxorus. Throughout her journey with Ash and Cilan, she learned to be more social and respectful, and trusting of humans, and gradually shed her "wild" nature. Her development was subtle, but still there.
Serena so far just seems like a stalker. What was her desire to leave on a journey? To find Ash. And then when she found him, she just assumed everything would go according to her fantasies, but this guy already had a mission in mind and was traveling. So she follows him, assuming she's part of the group, despite that never being her intention in the first place. Where's the interest? She has no spine.