The complaint isn't because that we don't like the new girls, the complaint is the more girls that are added, the more the dev time will be spread apart. Oxana and Maria were introduced just after coming to California, they still don't have their sex scenes. If there are 9 girls and 3 scenes per update, you'd get scenes for those girls every 3 update, while if there are 30, those girls will get a scene every 10 update.
When the game is completed, this complaint wouldn't exist anymore, but a lot of games with massive harems end up progressing in a snails pace, and worse, abandoned. While I don't think too many girls is that big of a deal yet, I do wish Dima would develop the neglected girls like Oxana and Maria before adding new girls to the harem.