This is going to be hard to answer, because what we consider gameplay is a simple term we use to try and describe what are complex moving parts. Gameplay isn't just interacting with the pieces. Chess is played in both the board and the mind, and video games are no different.
To illustrate this, I think adding a charge to Sharpcast is equivalent in scope to the situation that Kaiten was in, and if you're skeptical to how that can be, I wouldn't blame you. The two fulfill different purposes, but to me, what matters is whether or not the ability in question can be argued to have multiple positive uses, with which to say: Whether or not the ability has choice.
"Choice" in game design isn't the binary of "you do/do not". Choice in game design is the idea that when a player comes to a fork in the road during the game, you can list positives to both selections.
This is primarily why I and others say that Kaiten doesn't have choice, because the Kenki bar is ultimately a potency gauge, and the use of Kenki is therefore determined by what gives you the most potency per Kenki. On the surface level, this means Kaiten serves an important role for resource management - But the reality of the matter is that the deeper you dig for it, the less truth that actually holds. There is no "choice" in Kaiten, there's only optimization. There is no positive argument to make to skip Kaiten on Iaijutsu or Ogi. The fork in the road has one path, and one pitfall.
You don't make choices, you make mistakes.
As far as Sharpcast is concerned, Sharpcast and kaiten are similar in that Sharpcast is an action enhancer. It specifically targets Thunder, Fire, and Paradox. You use Sharpcast to enhance one of those. The difference being is that the intent and the result of Sharpcast isn't the same as Kaiten.
Kaiten enhances Iaijutsu, and any time that you could kaiten and didn't, you fell into the pitfall. Sharpcast on the other hand, due to the enhancement it provided (Guaranteed Spell proc), means that the result of using Sharpcast is ensuring a tool you might otherwise randomize into - In other words, it wasn't necessarily a DPS increase - It was the guarantee of an otherwise random event, and that random event had further uses.
1 Charge Sharpcast had choice. You had positive arguments you can make for delaying Sharpcast use, the design of Black Mage also allows pre-emptive use, as well as which spell you were goin to benefit from - Firestarter easing your AF timer, which had arguments to be made depending on the fight, or guaranteeing your TCloud, for more raw damage.
However, adding charges to sharpcast (And changing thunder) removes that. The only answer is Sharpcast Tcloud for your basic Sharpcast usage, and you have an extra Sharpcast just in case. The nuance and the choice is removed. That subtle mini-game within Black Mage's rotation is now gone, and we're talking about the result of what many could, rightfully, argue is a positive change, but you end in what is effectively the same result - There is only one answer for Kaiten, and there is only one answer for Sharpcast.
This also applies to adding charges to Triple Cast.
Black Mages changes don't necessarily change your inputs. Your standard rotation and the byways players come up with still exist, but it's the process in the backend that changes over the years, and it has made the job easier, less complex, and more forgiving, completely ignoring the actual mechanical changes of the job that have done the same. There is no debating this.
It is likely something you will not notice if you start the job now, because you will not have spent the time at each level cap to note how each cap increase changes this. This is the crux of the issue I have - These are, almost inarguably, positive changes to Black Mage, and yet I dislike them. I already wanted to dial some of it back in Shadowbringers with the addition of Xenoglossy and Sharpcast's recast reduction, because while Black mage is seen as the "Turret caster", they are nearly as mobile, and sometimes more so, than two of the Ranged DPS, ignoring just running around because they can.
Ask 10 different people what their job identity is and you'll get both 10 different answers.
To me, Samurai was a flexible melee attacker with only a few hardpoints in its rotation that you worked around, compared to, at the time, dragoon monk ninja who all had fairly strict rotations. The "Filler" rotation of Sticker generation was actually filler, because Hagakure was used to turn those stickers into Shinten. Kaiten and Midare were filler. Process that for a moment.
4.0 Kenki was the Shinten bar.
Perhaps that is where this apathy towards Shinten spam comes from. Just feels a little bit more like how it used to be.