Arcane Mage

[Skandranon]

- Curse of Shadows. +75% damage when grouping with Warlocks in the mid to late game. Yummy!

-75 resist is closer to +25% damage, but it's true that arcane overlaps with CoS in a positive manner.

Now I think people tend to assess resistance reduction on mobs and players by how often they see the word "resist" appear which is only a small part of the story.

Compounding this problem is the fact that both full-resists and spell misses display the word "resist", when full-resists are due to resistances and spell misses aren't.

Regarding the main question, yes, primarily Arcane mages are strong throughout the early game and midgame, and only weaken very slightly in the endgame. For certain Blackwing Lair encounters, Arcane mages are definitely the most useful mages.

For a lot of Molten Core, however, and some early endgame instance stuff, Arcane Missiles isn't a good choice because it's the most mana-inefficient of the three standard single-target nukes. Arcane mages run dry on every non-cursing boss mob in MC, whereas frost mages and even fire mages, to an extent, have enough juice to get through the whole thing.

Arcane Missiles also has a couple of other problems. First, it's channeled, and takes its cost at the beginning of the spell rather than at its completion. This means that if you start casting and you get knocked down, disoriented, or stunned, you're out the whole mana cost for only a few missiles. In contrast, if you get knocked out of any other spell, you lose time, but no mana.

Secondly, the way it's built ensures that it gets weaker as equipment improves. +damage equipment gives a percentage of the bonus to every spell, and for channeled spells like AM, the bonus is divided among every second.

Fireball: 100% of the bonus, 3.0s casting time with talents.
Frostbolt: 81% of the bonus, 2.5s casting time with talents.
Arcane Missiles: 100% of the bonus, 5.0s channel time.

Fireball gets 33% of equipment damage bonus per second. Frostbolt gets 32.4%. Missiles gets 20%. As your damage equipment grows, Missiles' relative strength continues to decrease. Even the resistance bonus of CoS doesn't help since vulnerability bonuses scale off the base damage off the spell. Using Arcane Missiles as a primary attack spell guarantees that you will be on the wrong side of Blizzard's item based progression basically forever. You must pick either Fireball or Frostbolt and Improve them to get decent single target damage at decent efficiency.

With 31+ arcane builds, what you're basically looking for out of either of the other trees is the best Fireball or Frostbolt you can build.

Fire builds generally go 5 Improved Fireball, 5 Ignite, 5 Impact and Pyroblast (to combo with PoM). Flame Throwing is a very popular choice as well since it offers several PvE and PvP advantages. Incinerate is also a pretty good deal for two points.

Frost builds generally pick 5 Improved Frostbolt and 5 Ice Shards. Cold Snap is not the objective in builds complementing 31 arcane, since you can only reset short cooldowns (frost nova, cone of cold). Cold Snap's real power is in resetting Ice Barrier and Ice Block, and you don't have either of those. The reason you get Cold Snap in such builds is because you want to pump points into Frost Channeling, a talent which is basically useless on the way up to 60 and very valuable thereafter. To get to Frost Channeling, primarily Arcane mages generally scatter four points between Piercing Ice and Imp Blizz as they desire and then pick up Arctic Reach and Channeling for a powerful and efficient Frostbolt.

Obviously, each of these builds can be adapted depending on how much you want out of your Arcane tree and your playing style. For example, you can pick up points in Improved Flamestrike or Burning Soul if you like either of those talents, or you could simply not take points in Cold Snap/Frost Channeling and get some more Focus or Subtlety.

One last point, though: the reason why you might want to boost Fireball and Scorch is because they're different spells and occupy different roles. Trying to use one like the other isn't going to work, though it will take quite a lot of experience to fully understand why.