In-Game Parser.

[Nominous]

This paragraph quite clearly shows why implementing a parser is not worth Yoshi's time. The rotation exists, but it's existence has no real impact on endgame fights due to mechanics; which makes the argument that a player must learn it blindly (and make no bones about it that's exactly what you are advocating, as your reasoning for learning it can be summed up as "for it's own sake") actively harmful to a player's performance because there's no context as to why. Even in your post you fail to point out why the concept of the rotation even exists within the context of the fight.

It's easy though. The rotation shows how a Job's abilities synergize, and how each one affects the other positively to use the whole potential the class provides. It's a concrete example of the value of each move.

And how much "betterment" is enough to have succeeded? No, "betterment" cannot be the end-goal of adding a parser, as that only has meaning in the transition. While perfection is unreasonable to expect, it is a fully formed idea that has concrete meaning within the context of the game and the raiding player base's expectation therein.

What about the other elements of social engineering? Adding a parser is all well and good, but you'll find that it'll have little effect if there's no reason to use it. So why not add reward mechanisms for actual excellence. Take the upgrade items like Oil of Time/Carboncoat out of the loot tables for all new content and only reward them to players that achieve performance milestones. There's now a connection between your performance and your progression.

Like the poster you were quoting said, a rotation past your opener is effectively a priority system. Understanding this priority system at the very least, will have you at baseline competence, and will get you through most non-current-raid content. It's the literal starting point as a DPS (let's call it crawling). Intermediate skills would be refining your opener to be optimal, not clipping DoT's, and understanding off GCD's and how to weave them in. Advanced would be things like when to multi-DoT, when to eat mechanics for more damage output, and making fight-by-fight specific changes to your rotation to do more damage.

Not understanding your rotation at the very least, makes raids/trials more difficult experiences than they need to be. In a game where others depend on you in order to succeed, it's irresponsible, and unfair to come to content and waste their time. That's regardless of the difficulty. That is to say...Don't go in someone's pony farm party if you're going to make it take 2 minutes longer due to your inability to hold your own weight.

Mechanics don't invalidate your rotation, they punish you for not understanding it. If you have to stop DPS for 5 seconds, and your buff is about to run out, but you continue your combo anyway when you're done with the mechanic, you're losing a pretty big chunk of damage. Things like this lead to difficulties in a fight. Making a fight more stressful due to a personal decision to stay uninformed (essentially, is what you're saying) is again, pretty unfair. This is not only your game, or your experience, it's other people's time.

As for re-working rewards to be performance based... that's more of a vicious idea than an in-game, personal parser. It not only promotes, but rewards people for doing whatever they can (mechanics be damned) to get high numbers. This is different from the idea of striving to be better because of personal reasons, or because you want to have healthy competition, or to hold your own weight. Also, assuming everyone is performing at 100% efficiency, some Jobs are known to be outliers (basically looking at MNK before NIN release/DRG buff) and would always get the reward. Let's assume that every class did the same damage. With certain end-game fights having RNG mechanics that force you to stop DPS, you'd be at the mercy of the game sometimes. It's a bad idea.

I have faith that this dev team, if no other, has the ability to implement a personal parser, no matter how thinly veiled, in a positive way. Not only in a positive way, but in a way that shows a player they can improve, and are doing well. Tutorials in this game are the next logical step, and if not now, then I don't see when they'd ever do it.
There's large importance to DPS, and I don't see that changing in the future. I don't see them making any non-story content any easier, and the further the game progresses and evolves, the less they're worried about the 'new' or 'uninitiated' player.