#1 - 2012/05/18 05:59:00 AMWarlocks have always been very efficient casters. Not because our spells are cheap, because usually they're quite expensive, but because we've always had an instant mana generator in Life Tap. Back in Vanilla we were one of the only classes with a mana generator, and while other casters were wanding we were capable of casting continuously.
Since then other classes have gotten their own forms of mana return, which is fine because nobody likes wanding. In MoP, Balance Druids have Eclipse and Innervate, Mages have Evocation and Mana Gem, Shadow Priests have Vampiric Touch, Shadowfiend, and Dispersion, and Elemental Shamans have Thunderstorm and Rolling Thunder. However, Life Tap is still the only instant mana return ability not tied to a proc, cooldown, or other mechanic.
That isn't to say that Life Tap is without cost. Life Tap has always had a health cost tied to it. In Vanilla, this was a flat cost with a flat mana gain. In BC beta, Blizzard attempted to change Life Tap to have a % health cost for a % health gain, similar to it is in MoP, but the community backlash against the change caused them to revert it before the expansion hit live. In Wrath, Life Tap's mana return was scaled with spirit, then later changed to scale with spell power. In Cata, Life Tap now costs 15% health, and returns 120% of that amount into mana. As you can see, Life Tap's moved from a static gain to one that scales.
As you could imagine, periodically reducing our health could potentially cause problems in PvE by burdening healers and in PvP by risking death. To counteract this risk, we've been given various self-healing abilities, both active and passive.
In MoP, things have changed rather significantly, and these changes have made us unsustainable.
First, there's the mana pool changes. Instead of mana scaling by Int, all casters have a static mana pool which scales by level. In addition to that, mana costs which were based on the rather small base mana pool have greatly increased since they're based on our full mana pool. So, our current level 85 Cata Shadow Bolt costs 2055 mana, and in MoP it costs 5500. Even though it's base mana cost is technically lower (from 10% in Cata to 5.5% in MoP), it costs nearly twice as much, and consumes more of a smaller mana pool. The end result is that we're spending more of our mana.
Second, Life Tap was changed to cost 15% of our health and give 20% mana. This change, combined with a now static mana pool, is just as bad as the attempted change back in BC. The problem with the BC change was that it was an equal % heath for an equal % mana. So, if our health outpaced our mana (which was common for 'locks due to passive buffs and talents), our mana gain was lower than our health lost. Our mana pool would scale with Int, but it was inevitable that our health would eventually surpass our mana.
In MoP, since our mana pool does not scale any more, the same problem happens as we acquire more stamina on our gear, even though the % health lost is lower than the % mana gained. As a result, as we progress our health cost gets higher, and eventually it will out-pace our mana. 85 'locks in raid gear are already surpassing the limit. Assuming we'll have 300k mana at 90, we'll out-pace the benefit at about 400k health, which doesn't sound that far off in raid gear. Increasing our mana pool won't really solve the problem either, as that would just increase mana costs on spells.