Diminishing Return on Stats

[Gamemako]

One thing oddly absent from this discussion: abilities also diminish the relative returns of certain stats. Automatic critical hits and other flat critical hit bonuses (Internal Release, for example) reduce the relative returns from the critical hit rate stat. Also worth noting that Determination appears to also suffer diminishing relative returns to strength; i.e. it is at least partially additive with strength rather than multiplicative.

It's not. That's only a reflection of the UI truncating numbers. A guy on reddit showed the detailed tests of Rez (8s base spell) and the cast time appeared to be reduced in 0.1s increments at the same ratio as a 2.5s base spell was reduced. E.g. the SS formula is probably a straight % reduction in cast time, with the game UI truncating.

As a note, this reduction is applied after most other bonuses and is additive with them; for example, Greased Lightning reduces your GCD natively to 2.125s, and skill speed still reduces by 0.00069s per point thereafter (rather than 0.00059, which it would do if it were applied beforehand and then reduced by the 85% factor from GL3). I believe Fey Light at the very least is an exception, acting directly on the Skill Speed stat itself.

However, the benefit of the acceleration requires a LOT of the stat to be stacked -- much more than is reasonable without killing your TP bar, or mana bar for most classes.

This is true, though not really the reason everyone hates skill speed. The damning thing about skill speed is that it fails to affect autoattacks, off-GCDs, and DoTs (barring situations where reapplication is naturally delayed by things like Jump), which in total comprise upwards of half of total DPS for all DPS jobs but BLM. Accelerating returns can't touch that one way or the other. Until they fix it so the stat affects autoattacks at least, the only job deliberately taking it will continue to be a tank. If it did affect at least autoattacks, it would be nearly as valuable as any other stat for many jobs (especially MNK).

[EasymodeX]

no we shouldn't understand "increase of DPS in %".

That's the context of the discussion of MMORPG damage optimization with incremental stats/gear. So yeah.

If I ask you, durng an exam "is DPS linear in crit" and your answer is no, you failed the question.

This isn't math class.

If anything, this is economics.

The damning thing about skill speed is that it fails to affect autoattacks, off-GCDs, and DoTs [...] Accelerating returns can't touch that one way or the other.

Well, the fact that it doesn't affect AAs and oGCDs simply sinks the initial value of SS for classes that have those. The acceleration still happens and is still relevant. Specifically, Monks, due to the GL stacking as you noted earlier (increasing the initial value for SS), get just about / almost as much value from SS as they get from crit (crit gets chunked down with diminishing marginal returns on normalized value due to the BS autocrits and traited IR that you also mentioned).

[Gamemako]

Well, the fact that it doesn't affect AAs and oGCDs simply sinks the initial value of SS for classes that have those. The acceleration still happens and is still relevant.

I'm just saying that the TP really isn't too much of an issue in practice, but the other disadvantages pretty well relegate the stat to niche status. Adding autoattacks would at least give MNK another stat to consider; right now, DTR is twice as valuable as either alternative.