Technically you can get both scenes, you will need to change the Affection and lust points before the scene is about to trigger. If you want both the scenes then I have mentioned the points that you will need to get the scene to trigger.
But in my opinion, Kasie's lust route is very rewarding, and due to the pace of the story it doesn't seem out of place. Kasie's behavior is changing bit by bit and through actions of her own and the events happening around her, making her corruption journey worth it. And all of this is coming together nicely due to the story. Additionally, it's very interesting to see the outcome of your choices and the impact it has on the scenes that are being triggered due to those choices. Many VNs do it but most of them just have important choices that have an impact on the story and the scenes, but in this game, certain choices may not look like it but they have an impact on future interactions and story.
This game is a breath of fresh air in the long line of games that go from 0 to 100 in terms of fucking each and everything in a mere 10 mins of gameplay. I am very happy to wait for the story to progress the way Dev has envisioned because so far I am not at all disappointed.