Sorry for the baity title, just want to draw attention to a better solution than the merging of Senei and Guren.
In image form!

Hope this helps get the idea around so the devs see more of it in place of the common idea that I and many others have had of merging Senei and Guren.
Do this, don't remove Kaiten.
Reduce CD drifting. Reduce the skill floor. Maintain the skill ceiling! Much better.
There's no reason Senei and Guren should exist as they are currently.