Unpopular opinion, but I understand "why" they removed it and therefore don't blame them for that reason.

Unless I am wrong, there wasn't a single instance where you'd NOT use Kaiten before an Iaijutsu, not using it on one was basically a failstate and using it on old combo finishers as well, given the potency difference. This is different from buttons like old Dark Arts, Life Surge, Reassemble etc. where you did use instances of the skills you usually enhance as their unenhanced version, save for Carve and Spit, that small MP vs losing 350 potency was laughable.

So while we may have liked it, it was basically a soft-mandatory button press before every Higanbana / Tenka Gokken / Midare Setsugekka if you played seriously as not doing so was a fairly sizeable damage loss if you repeated it over time. So I can see why they dropped it out of the sky and called it Button Bloat, even if worse skills like Shoha II exist.

We need different Kenki spenders, but I feel like Kaiten wasn't it. What I do miss however is Hissatsu: Seigan instead of just gaining flat +10 Kenki on Third Eye.