Character growth, overcoming flaws, fears, a change in personality. We've seen nothing from anybody but Mijumaru up until now. Most of the pokémon on Ash's team still feel like strangers at this points where they've all been on the main cast for at least 15 episodes
Zuruggu and Tsutarja have personality, but both lack developpement, battles and screen time. Hatoboh
doesn't have much of anything, still nothing really definitive personality wise, none of the traits shown as a Mamepato
have appeared since evolving, and lacks developpement, battles, screen time. Pokabu
has enough battles, but still nothing on the personality or developpement side.
So yeah. All of them are incomplete at the moment. Mijumaru is the only one that's really been focused on. Adding one more pokémon is only gonna aggravate the situation.