What makes a class needing Crit or Det or D.Hit in priority? (mainly about MCH)

[Idolon]

Black Mage is one of the few classes in FFXIV that REALLY wants speed above all else because of how our casts are slower than the GCD.

It's not so much the length of casts that makes spell speed good for BLM, but the fact that every damage skill BLM has is on the GCD. Most other jobs do a significant portion of their damage through off-GCD abilities with fixed-duration cooldowns, and skill/spell speed does not affect those at all.

[EllieShadeflare]

It's not so much the length of casts that makes spell speed good for BLM, but the fact that every damage skill BLM has is on the GCD. Most other jobs do a significant portion of their damage through off-GCD abilities with fixed-duration cooldowns, and skill/spell speed does not affect those at all.

Well, that also helps too. Doesn't hurt that some of our hardcasts are longer than the GCD (especially our bread and butter, Fire IV).

[Rongway]

Well, that also helps too. Doesn't hurt that some of our hardcasts are longer than the GCD (especially our bread and butter, Fire IV).

That really doesn't matter, because even if you had so much more spell speed that the Fire IV cast time was absurdly fast like 1.5s, it would still be longer than the GCD.

Idolon is right in attributing it to how every single offensive action a BLM can take is a GCD action. 100% of BLM damage is on GCD, so if cast times drop by, say, 5%, BLM damage goes up to 105.26% (1.0 ÷ 0.95). Compare to another DD job that might do 70-80% of damage on the GCD and 20-30% off it, a 5% cast time reduction only results in 103.68-104.21% damage (0.7 ÷ 0.95 + 0.3) ~ (0.8 ÷ 0.95 + 0.2).

[EllieShadeflare]

That really doesn't matter, because even if you had so much more spell speed that the Fire IV cast time was absurdly fast like 1.5s, it would still be longer than the GCD.

In a sense, you're right, but I was more nudging toward Fire IV's relationship to Astral Fire (or rather, its inability to refresh that). Mostly, Fire IV's design isn't that well balanced with the new Enochian mechanic as it is, and only Spell Speed can solve that to any extent.