I'm a samurai main - I've played all the jobs, and samurai is my favorite - by far - and not for the aesthetic, but for the gameplay. I've never even visited the forums previously, but this change is so egregious that I felt compelled to speak out.
The fact that samurai has a variety of resource-based OGCDs that they get to use frequently isn't a trivial coincidence about my favorite job - it's WHY it's my favorite job. I like getting to use OGCDs often, and monk hardly ever gets to. I don't like having to babysit cooldowns, and dragoon OGCDs are almost entirely cooldown-based. Reaper plays much slower than samurai besides enshroud. Ninja has a significant amount of cooldown babysitting and the resource they do have is a mindless spend - effectively what samurai's would become if Kaiten is removed. Samurai is my favorite job for a reason, and the removal of Kaiten works directly against the reason I like the job in the first place.
Removing Kaiten would effectively turn kenki into just a Shinten/Kyuten gauge with the rare exception of needing a tiny bit for movement or pooling it for burst. We already lost Seigan. We no longer have to pool additional kenki for Senei/Guren. Losing Kaiten as well would make samurai resource management and usage effectively mindless - just use Senei/Guren if available, else spam Shinten/Kyuten - no more using the right OGCD at the right time - no more pooling before Iaijutsu. The removal of Seigan was a step away from what I initially liked about samurai, and the removal of Kaiten is a massive leap in the wrong direction for my tastes.
What was this change meant to accomplish? If it was aimed to reduce button bloat, there are FAR better targets for that which have already been pointed out all over the forum, youtube, etc - changes that could lessen button count without actually removing anything. If it was to reduce APM bloat, it won't achieve that either since Kaiten only costs 5 less than Shinten/Kyuten - meaning APM will be almost identical - just more monotonous.
Who was this change meant to appease? Were samurai players calling for a rework? Was anyone asking for Kaiten specifically to be removed? I, for one, thought samurai was in a fantastic place. I loved the job in Shadowbringers, and while I lamented the loss of Seigan going into Endwalker, I loved the extra charges for Meikyo Shisui and Tsubame-gaeshi (because this reduced the importance of cooldown babysitting, which aligned with why I liked the job in the first place). Removing Kaiten, conversely, actively works AGAINST what I like about the job.
Whatever the reason for this change, please consider that it may be a reason why players who like the job DO like the job. A job isn't isn't too fast, nuanced, or complex if the speed, nuance, and complexity are what its players like about it. Please don't arbitrarily rework kits that people love as-is.