Hi, no offense but it seems like you haven't played a lot of adult games. Summertime Saga and Once in a Lifetime belong to different genres. As you already mentioned, Summertime Saga focuses on freedom and variety while Once in a Lifetime focuses on story. It's intended this way. Both games are very popular in their respective genres!
You should also know that this is a completed game and any major improvements you suggest are most likely not going to happen.