So an oft-overlooked aspect of the Kaiten argument, particularly here, is that Kasha and Gekko combos now generate a flat 20 Kenki regardless of positional. This was a small change that snuck in with the EW release and it didn't accrue much in the way of fanfare; after all, if you did things "correctly" then you would always have the maximum amount of Kenki available, yes?
Except this was simply another brick in the wall, although we didn't know it to be such at the time. Back when there was a variable amount of Kenki generated (50, 55 or 60 per full 8 GCD combo cycle) you had to factor this into the equation of your gameplay. You no longer were going to be guaranteed 60 Kenki per cycle. Yes, True North helped, and yes hitting the positionals themselves wasn't hard for the most part, but there were still fights that pushed you into bad spots occasionally where you would be forced to either eat 5-10 less Kenki gain or else alter your GCD flow (such as by using a Yuki+Haga GCD shift at an earlier time than you normally would).
At the time that the positional requirements got shifted from increased Kenki gain to the current state of boosted potency and a flat 10 Kenki, well, it didn't make much of a difference. Because, again, it was easy enough to rationalize "well you should always be hitting your positionals" as an excuse. Now, with the removal of Kaiten - and with the context of the apparent future of job design in this game - it's clear that the Kasha/Gekko changes weren't simply a pure "accessibility" change, but rather were the first step to the ultimate destruction of Kenki as a resource to be managed. You've no doubt seen the many comments now about how Kenki is functionally useless. Many people have rightly referred to Kenki as the Shinten Gauge now, while weaving Gyoten into the opener and sometimes even the burst window is now considered optimal due to the loss of Kaiten and the ppK nerfs Shinten received.
All of this ties into the "PLD" MP management comparison you made. But that isn't a justification for removing Kaiten or otherwise keeping the current changes; it's a justification for reverting the changes and bringing back Kenki management as a real aspect of the job, up to and including the reversion of Kasha and Gekko Kenki positional gains and the cost reduction on Senei/Guren. As it stands now, yes, Kaiten was much more braindead than it was in ShB and SB, but it still did at least require at least one brain cell to use correctly. The reason why it was so braindead was because SE changed things to make it more braindead. Whereas before you had to always keep one eye on your Kenki gauge and make on-the-fly decisions based on how a fight went (icicles in E12s, Emerald Weapon/Ruby Weapon EX's, SoS EX 5 elements, Light Rampant in E8s, to name a few) SE removed a big chunk of that with the 6.0 change. Then they removed what was left of it with 6.1.
Sure, a new player can probably pick up SAM 6.1 and play it and notice any problems, but you can make a comparison there about a lot of things. I can go to McDonald's and get a Big Mac, and while it'll satisfy my hunger it's nowhere near as good as a nice AAA grade Angus burger cooked over an open flame. SAM could be so much better. It WAS so much better. Making excuses for the current state of SAM isn't the way to go; this needs to be a moment of sea change. This needs to be the point where the players say to the devs that "easy" design for them shouldn't be the governing principle. Of course as time goes by there will be problems with iterating on jobs but that's not a reason to gut something that was fun, engaging and performed perfectly fine! Laziness is never an excuse, and I call out as much in a post I made here:
https://forum.square-enix.com/ffxiv/...ZY.-Here-s-why
Point being there are so many people, new posters to the forums, who have never posted here before, and they are pissed about the changes. JP has had more feedback and forum activity in the past month regarding this change (and many 6.1 changes in general) than they had in the entirety of 4.0 to 6.0. This can be a turning point where we, as the players, tell the devs that not only were the 6.1 changes bad but that the general direction of job balance needs to be changed too. Not just for SAM, not just for NIN, but for MCH and SMN and tanks and healers too. I have no delusions about some kind of magical Heavensward revival or something, but the solution for a player who wants engaging gameplay should not be "go play ultimate." Perhaps that quote was taken out of context but the core gist of what underlies it still remains; jobs need to be engaging in-and-of themselves regardless of the difficulty behind any content you're doing. A player shouldn't need to seek out harder fights to feel engaged by their job as the jobs should be engaging enough at a core level.