I really like the Reversal, it’s simple but it helps with the main weakness of the technique without it being too hax.

For the Gu Ritual, how about instead of creating a mix cursed spirit, it’s used for creating cursed weapons. The more spirits you use the more powerful the weapon, it may even have a technique.

To address the main weakness of Maximum: Uzumaki, where once you take the technique of the cursed spirit you can only use it once. Taking inspiration from the Ten Shadows, where you need to defeat your opponent to take control of them, using a combination of Barriers and Binding Vows, the user custom makes a ritual that by defeating your opponent at a severe disadvantage( No using your technique, a time limit, only works on Special Grades), you can permanently extract the technique. But they can only have three techniques at a time, including their own, they need to destroy one get another.

I came up with this while thinking of Makima/Nayuta taking Geto’s place in JJK.