A Tale of Two Frosts (Death Knight, to be Clear.)

While casters can pretty much pick whatever combination of weapons, off-hands, and shields will provide the greatest spellpower, most physical specs are limited to a single load-out - there are sort of genres of weapons that they'll use, but a Retribution Paladin, for example, is always going to be using a two-handed strength weapon, and an Assassination Rogue is always going to be dual-wielding agility daggers.

While Monks are kind of a whole other story (and one I have far less experience with,) there are two melee DPS specs that have options for weapons.

Fury Warriors can go between what used to be called "Titan's Grip" and "Single-Minded Fury," choosing to go with two-handed or one-handed weapons in each hand. Various passives ensure (or at least try to ensure) that, despite having less stats and lower base weapon damage, a Fury Warrior who chooses to use smaller, faster weapons will still be able to do the same amount of damage. The Fury rotation remains more or less the same - you still want to stack up critical strike rating so that Bloodthirst triggers Enrage as often as possible. The two styles play very similarly, and really only vary in terms of rhythm.

Frost Death Knights, however, feel quite different depending on your weapon choice, to the point where they're nearly different specs. These used to have their own fun names - Threat of Thassarian for dual-wielding and Might of the Frozen Wastes for two-handers. (Really, I wish they'd bring back some of old passive abilities that got merged into active abilities or turned invisible. It provided flavor and it also made it way easier to understand a spec.)

The central mechanic of Frost is Killing Machine - a proc activated on occasion by (main-hand) auto attacks. This makes the next Obliterate or Frost Strike a guaranteed critical strike. The big reason why this divides Frost Death Knights is that other passives buff one ability or the other depending on what loadout of weapons you're using.

Those who use a two-handed weapon focus on Obliterate, a two-rune, purely physical attack that hits like a truck, particularly when you crit with it. Dual-wielders instead buff Frost Strike, a... strike that deals frost damage and costs runic power rather than Runes.

This difference creates a kind of avalanche of differences. The Frost mastery simply increases frost damage dealt by the Death Knight, which makes it more valuable for Dual-wielders, but it does nothing for two-handers' most powerful attack. Because Dual-wielders can safely invest more in Mastery, they then deal greater AoE damage through Howling Blast - one of Frost's most potent AoE tools.

Thus, there's an inherent imbalance - Dual-wielders will suffer less if they gear for AoE than Two-handers. In fact, during Mists of Pandaria, a Dual-wielder who stacked up enough mastery could simply spam Howling Blast rather than ever spending runes on Obliterate, using the orphaned Unholy Runes for the occasional refreshing of Blood Plague or throwing down a Death and Decay. Their rotation was essentially identical for single-target and AoE situations.

Before we ask how to fix this, we should wonder whether it should be fixed at all. Would it be ok for Frost to be better at AoE when dual-wielding? Perhaps two-handers could be compensated by having better single-target balance - but that opens a can of worms. Given that DPS matters most on bosses, and usually it's single-target damage that counts the most (though perhaps more accurately it's single-target damage that people pay the most attention to) it could be dangerous to enshrine one style over the other for that situation.

There are a couple issues of "good feeling," though, that are of course very subjective. As someone who prefers the rhythm of two-handed frost, it's always a little frustrating that Mastery doesn't affect my biggest ability. Usually they make Mastery more interesting than a simple "+damage" stat by having it affect only your biggest abilities - like Retribution's Hand of Light.

But the issue with Frost's Mastery is also that it makes gearing within the same spec pretty significantly different. If you want to swap out your weapon load-out, you'll need to re-gem and enchant your stuff to maximize your damage. It also makes Frost's stat attunement, Haste, kind of anticlimactic for dual-wielders who focus on Mastery (at least last time I checked, which was admittedly a while ago.)

The Archimonde trinket in Hellfire Citadel gives Obliterate a Frost Component, and I could see this being a kind of "try out" for a change to the mechanic. If Obliterate dealt Frost damage, it could make Mastery a good stat for all Frost Death Knights, and would do a lot to balance out their AoE damage.

Another alternative would be to unify the preference of Obliterate or Frost Strike - if both types of Frost preferred Obliterate (which has a ton more flavor than Frost Strike,) neither would be pushed to stack mastery. On the other hand, this difference in style is something that makes Frost a fairly unique spec, and surely there would be people upset that their style got taken out in favor of the other one.

A modification to Obliterate - either adding frost damage or making the entire thing do frost damage (though it's the only physical ability you use other than auto-attack) - would do a lot to emphasize the "frost" aspect to Frost Death Knights. And once they do that, they could start working on getting the "death" aspect back into the spec.