Strength gives 2 melee AP per point to druids, paladins, warriors, and shamans, and 1 AP to other classes.
Agility gives 2 ranged AP to hunters, 1 ranged AP to rogues and warriors, and 1 melee AP to hunters, rogues, and druids in cat form.
For druids in bear form, warriors, shamans, and paladins, it gives no melee AP, just crit chance and dodge chance.
Besides hunters and rogues, if you use melee, you’re going to want both strength and agility. This is reliant on correct itemization - which I’m not arguing that gear is incorrectly itemized, just stating that most classes are looking at more than one stat still for dealing damage. (And even for rogue and hunter, they’re not just looking for gear that gives agility, but agility and attack power.)
If you roll in pure greens that are just “of (Element) Wrath,” you’re going to severely gimp yourself in terms of spell hit, spell crit, and your mana pool, for not a massive amount more spell damage. I just spent some time rolling up a phase 1(of Classic) mage in mostly pre-raid BiS on a gear planner, then compared it to almost the same gear, but replacing pieces with “of Frozen Wrath” gear where it would result in more spell damage. The results, unbuffed?
- 2660 health(147 stamina) drops by 300(30 stam) to 2360.
- 4398 mana(231 intellect) drops by 615(41 int) to 3783.
- Spell hit drops from 11% by 5% to 6%.
- Spell crit drops from 9.08% by 2.69% to 6.39%.
- Frost damage increases from 424 Frost damage by 59 to 483.
And this is only on gear that would get at least some increase to Frost damage, not drafting up a full pre-raid set of nothing but “of Frozen Wrath” gear. Doesn’t really seem like a great idea to forsake other stats - including int - for spell damage.
I also tried this for SoD at level 25 with BFD gear, and I know the play for mage in BFD is Arcane right now, not Fire, but there’s more non-green gear that gives Fire damage specifically than other caster specs. My results:
- 655 health(52 stamina) drops by 80(8 stam) to 575.
- 2511 mana(154 int) drops by 630(42 int) to 1881.
- Spell crit drops from 7.52% by 2%(all attributed to int; no spell crit% gear is present in either) to 5.52%.
- Fire damage increase from 108 by 43 to 151.
Invoker’s Mantle and Cord each give 7 spell damage and 5 int. Combined, that’s 14 spell damage and 10 int. Combining the shoulders from the Horde version of Allegiance to the Old Gods(6 int, 2 stam, 5 spell dam) and Ghamoo-ra’s belt(8 int, 8 stam) comes out to 14 int, 10 stam, 5 spell damage, or 4 more int and 10 more stam for 9 less spell damage. If you’re playing Alliance, you can instead go for the shoulders off Lady Soveress(10 int, 5 spi), giving you an extra 4 int at the cost of 2 stam and 5 spell damage.
I won’t be dishonest and say casters aren’t in a great place right now in PvE; they’re significantly behind most melee(I think enhancement shaman is the sole outlier), they’re doing less damage, and many of them have the potential to go oom. On top of that, the ones performing best are relying more on spells granted by runes - all of which are base mana % cost, rather than a flat cost with multiple ranks - to deal the lion’s share of damage. That having been said, itemization later in the game balances it out far more than it is currently sitting at, and tying spell damage to intellect would either have to be so miniscule that it’s essentially worthless, or it would be so good that you may as well remove spell damage on gear, as it’d be far more effective at increasing your damage and your mana pool to simply stack int.