This is not a guide, because Icy Veins does it so much better. This tries to be an analysis why Arcane failed in MoP. The simulations tell that Arcane is one of the top specs - in a Patchwerk fight. In reality Arcane is one of the worst raiding specs in MoP in patches 5.0.5 and 5.1
Arcane differs from the other mage specs because Arcane's mastery [Mana Adept] ties your dps to your mana. A spell casted by a Fire or a Frost mage will do the same damage at 100% mana or at 5% mana, but an Arcane mage gets a buff based on the amount of Mastery points he has and the amount of mana he has left. So in order to maximize your dps you want to stay as close to 100% mana as you can.
However it is not that easy to stay at full mana. In MoP mages have a fixed 300k mana pool. The first Arcane Blast you cast takes 4,500 mana, but every stack of Arcane Charge increases the mana cost by 5,625 (125%).
1st Arcane Blast takes 4,500 mana (no Arcane Charges)
2nd Arcane Blast takes 10,125 mana (1 Arcane Charge)
3rd Arcane Blast takes 15,750 mana (2 Arcane Charges)
4th Arcane Blast takes 21,375 mana (3 Arcane Charges)
5th Arcane Blast takes 27,000 mana (4 Arcane Charges)
6th Arcane Blast takes 32,625 mana (5 Arcane Charges)
At six stacks the cost of one Arcane Blast spell is 38,250 mana - that's 12.75% of your mana pool so you don't normally want to cast Arcane Blasts at six stacks. But even getting to 6 Arcane Charges using only Arcane Blasts takes 111,375 mana - about 37% of your mana pool. And that was without Arcane Power buff which adds a 10% mana cost to all damaging spells.
Of course you will gain some mana during the casting. In MoP your combat regeneration is 15,000 mana every 5 seconds so let's say it is 3k per second. Arcane Blast takes about 1.85 sec to cast so six casts take around 11 secs.
Mana used in 11 secs = 111k
Mana gained in 11 secs = 33k
I think it is easy to see that you will go OOM very soon if you just keep on casting Arcane Blasts. This is something Fire and Frost mages won't face no matter how hard they try to spend their mana. The level 90 talents are just buffs for them even though all three level 90 talents are designed to increase the amount of mana you can get:
- Invocation makes your mana go like a roller coaster so it is not good for an Arcane mage
- Incanter's Ward increases your mana regeneration by 65%. Based on my experiences this is not enough for Arcane. You will end up Evocating to get back to full mana unless you break the Arcane Stacks before 6 stacks.
- Rune of Power increases your mana regeneration by 100%. It is the best and basically the only choice for Arcene (of the poor options).
What are the biggest problems for Arcane:
1) Tier 6 talents. Mana regeneration and dps buffs are in the same talents. If the dps buff didn't exist then there would be some room to cast without Rune of Power - or the other way around. Now without Rune of Power you will lose both dps and mana.
2) No instant spells to refresh Arcane Charges. Yes, Arcane Explosion can do that, but even with the glyph the range is only 25 yards. The other instant spell, Arcane Barrage will break your stacks.
Where Arcane is good?
If we are talking about raid bosses I have seen only one situation where Arcane is better than the other mage specs: Elegion sparks.
What you can do to improve your dps:
1) Stay within 25 yards of the boss. This allows you to refresh the Arcane Charges using Arcane Explosion.
2) When you create a Rune of Power stand at the edge of it. Several boss mechanics (like Amethyst Guardian's Amethyst Pool) allow you to use the same Rune of Power if you didn't stand in the middle of the ring.
3) Always try to get to 6 stacks of Arcane Charges with 2 procs of Arcane Missiles. And after the missiles refresh Nether Tempest because you might get one more Arcane Missiles proc.
4) Write to WoW forums and demand that Blizzard does something.