The easiest of changes would be just to bring back Kaiten as it was before, but instead of making your next Iaijutsu 50% stronger, just make it guarantee a critical hit instead, while buffing shinten a little bit to balance the kenki cost of Kaiten.

As for button bloat, Ikishouten could turn into Ogi Namikiri which now turns into Kaeshi Namikiri anyway.
Shoha I is replaced by Shoha 2 with a buffed up potency. I don't think anyone would mind not having a single target Shoha, but instead just one Shoha for both 1 target and for AoE.

If the button bloat is real, which I don't think it is, you can even combine Guren and Senei into one, by asking the community which animation is better in a google forms or something. Or just pick one and buff it up for single target while adjusting its AoE fall off.