I feel like if anything the development is more focused on other characters, Ataru, Kyouko, or Kita. But on the two focus characters of Elly and Wanko, I'm not sure development is really needed for them, like yeah Wanko is an immature goof to a fault, but that's something that'll be she'll work on years down the line and not necessarily in the timespan the manga took place. That said, the ending feels clearly axed and its why it sorta feels like the developments with Ataru and the side characters feel cut short.