The issue that it was addressing wasn't the joy-factor. It was the justification of the system itself, which is what you were largely asking about ("Why does it exist"). If you tighten the leash on TP such that running out of it becomes easier/more common, it has a greater justification since it is a more readily limited resource that has to be paid more attention to.
As to the "innate recovery mechanism" that you say the classes don't have, they all have the same one: the baseline TP regeneration. Yes, it's not all that impressive or interesting, but it's still *something* and, honestly, it's *enough* given that, for absolute resource consumption neutrality, you only have to sacrifice roughly one out of every 4 GCDs. It's not so much that it's frustrating or bad on its own, but moreso that it's simply *boring*.
I said that to demonstrate why we have it, even if it means nothing 99% of the time. TP could be completely removed without having a substantial effect upon a *vast* majority of gameplay, but that doesn't mean that it doesn't have a good reason to exist.To remove it from the game completely, I don't know.
Most of what I was saying there was purely hypothetical or abstract. Resource models for games are always interesting things to analyze/compare/discuss. I was honestly surprised that ARR went with a variable size resource system for casters as opposed to the static resource systems that are becoming more and more common with casters in existing games. It matters less to BLM and SMN because, since they don't stack PIE at all, they have effectively static resource pools, but, for the healer classes, it's going to create some interesting issues down the line. Without intervention at some point, resource pools for healers could (and would) get large enough that healers stop using their lower level heals completely because their resource pools and regeneration (which is based upon max mp) would be large enough to soak up the inefficiency. I'm already seeing it to some extent with full i90 healers. It's one of the things that's always been problematic about variable size resource pools: they create drastically different use paradigms at different gear levels. Most newer MMOs have recognized this and are moving away from them and replacing them with static (or, at the very least, variation that is independent of gear).
Complexity and increased skill ceilings do not automatically translate into higher player satisfaction (which is what we're going for here). There's a higher relative skill ceiling on a WAR than there is on a PLD because the WAR is more active and has more options/stuff to think about than a PLD does, and yet, even though WAR has the more complex playstyle, many people still find PLD to be the more rewarding job to play. Just because there is more that *could* be done with it doesn't mean that there *should*.I just feel like there is a lot left on the table with MP and TP which could raise the skill ceiling of the classes in this game, and also make players feel more rewarding.
I think your problem has less to do with TP and more to do with the overarching implementation of ARR's resources. It's pretty difficult to come up with a way to directly "complicate" a standard resource system like TP or MP without making it either arbitrary or outright annoying: RNG based regeneration mechanisms (e.g. regain X TP when you block or parry), regeneration mechanisms you have no ability to influence (e.g. regain TP whenever you are hit by an attack; since some enemies have high attack speeds while others have low attack speeds; you would have a glut on some fights and be starving on others), toggled consumption (e.g. turn on X ability to increase TP cost and damage), etc. While those changes make resource management more complicated and *somewhat* more compelling, they really just end up just making the system less predictable and enjoyable in the process.
All of the DoW classes use the same basic resource paradigm (ability consumption with consistent regeneration) with the exception of one: WAR. WAR is a job with a hybrid resource, which makes it different and more complex than straight TP. Because it's directly controllable and predictable (you generate Wrath through your own actions in an entirely predictable way), it's more compelling and interesting than what you'd get arbitrarily manipulating the TP system to complicate it. PLD gets close with Riot Blade and Flash, but not enough is done with their MP to really qualify.
As such, it's not so much that TP is a bad/boring system. It's that TP *alone* is a bad/boring system. PLD could be made a fair deal more compelling by actually integrating MP into their fundamental playstyle more. MNK could probably play around with certain powerful abilities that consume Greased Lightning stacks. I can't think of anything off of the top of my head for DRG or BRD, but it's entirely feasible for them to receive an additional secondary resource to compliment TP (possibly "jump charges" for DRG that are generated by some attacks and by their jumps; still not entirely sure about BRD). It creates the compelling resource management experience you're looking for without arbitrary complication of the existing resource, plus, it lets you create the feel you're looking for with the specific job without unintentionally impacting the others.