I think Ako and Raita's development was just fine. Ako went from being a self-absorbed, naive teenager who was only interested in money into a pretty strong heroine. I mean, she goes through a lot: her first love dies, her long-lost teddy bear that she coldly threw away literally dies for her and she becomes one of the most loyal Jetmen after the team temporarily disbands.
As for Raita, he thinks he's in love with Kaori but soon realizes he'll never have a chance with her and moves on, and he learns to work with other people instead of just living happily with his vegetables. Raita is sort of the shafted member of the group, but he still gets more development than entire Sentai teams (Maskman, Zyuranger, Gekiranger based on what I've seen).