The change to Scourge Strike introduces the following problems. But first, lets talk about its current problems.
Current:
1) Scourge Strike does damage roughly equal to two Blood Strikes, meaning Reaping is not taken in an already very bloated tree.
2) Scourge Strike does not do enough damage in PvP to qualify as what many would call “viable burst,” and thus forcing Uh DKs to pair with a Mortal Strike class or a class that can provide on demand burst to be viable in arenas (aside from Shadowcleave, one of the few remaining viable DK comps).
3) Scourge Strikes already low, but arguably acceptable damage is heavily penalized by disease dispels, which is why many DKs have resorted to creating builds that focus on high RP generation for Death Coil and use only disease applicators in leu of FU attacks because it increases disease uptime and does not rely on keeping diseases up as much. DKs do not play Shadowfrost because it is overpowered, this is a myth, they play it because it covers the massive limitations created by the totem stomp change and the Scourge Strike damage nerf.
These are the problems created by the 3.3 incarnation of Scourge Strike. I will back this with some math done by Dracosz of Executus.
1) A larger percentage of Scourge Strike damage is reliant on maintaining disease uptime. This is a problem when we have trouble keeping diseases up even with a wacked out build that only uses FU runes for disease applicators.
2) The Scourge Strike change makes SS benefit 100% from Armor Penetration, which accomplishes the goal stated by Blizzard. However, this seems to contradict the idea that Armor Penetration is disappearing on gear completely with the release of Cataclysm. This means that with the release of Cataclysm, Scourge Strike will simply be penalized by armor with no gain since we will not be able to obtain ArPen, and I highly doubt Unholy of all three of the specs will be receiving Armor Penetration as a Mastery bonus.
3) Scourge Strike does more damage in PvE now. This makes Reaping worth it, but unfortunately, Unholy is bloated and finding the points for Reaping isn’t exactly easy, and Death Knights arguably did not need help in PvE.
4) Scourge Strike does less damage against Mail armor and higher in PvP. This is a nerf to an ability that was critting for 4k with 3 diseases up. Death Knights arguably do not need a PvP damage nerf. First sentence is fact, second is opinion.
5) Scourge Strike does more damage against leather and cloth wearers. Casters are not our problems in arenas.
6) There are likely to be a large number of detrimental bugs with this change. For example, I am willing to bet the Shadow Damage portion of the ability will do zero damage if the Physical Hit is absorbed by a Power Word: Shield or Ice Barrier.
Here is some math to demonstrate the new 3.3 damage compared to the current damage.
Weapon Damage - 3000 (I like to work with 3000 because it shows up very clearly)
*NB I use 3 diseases as an assumption and I do NOT include Black Ice which would increase the damage on the PVP by 10%
Current Scourge Strike Mechanics
PVE
.78 * 3000 + 432 = 2772 damage no resilience non-mitigated
2772 * 2.3 = 6375.6 damage no resiliance crit non-mitigated
PVP
2772/1.15 = 2410.43 damage mitigated (resiliance)
6375.6/1.15/1.25 = 4435.2 damage mitigated crit (resiliance)
New Scourge Strike Mechanics (Presumably)
PVE
.5*1.2 = .6 (Coeffeicient for Scourge Strike Baseline Physical Damage)
.6*3000+452 = 2252 Damage
Bonus Shadow Damage = 2252 * .75
Total Non Crit New SS damage = 3941 Damage
Crit: 2252 * 2.3 = 5179 damage
Crit Bonus shadow Damage = 3884
Total Crit New SS damage = 9063
/* Work In Progress, I'm fine tuning a bit of this
PVP
// Assumes 15% Damage Reduction Passive from Resilience and 25% Crit Reduction from Resilience
PLATE HEAVY MITIGATION (65% Physical Reduction)
Initial Damage = .35 * 2252 = 788.2
Shadow Damage = 788.2*.75 = 591.15
Total Hit = 1379.35 (Factoring In Resilience)
Crit Damage = 1379.35*2.3/1.25 = 2538 Damage
Delta Hit:-1392.5
Delta Crit:-1897
PLATE/MAILW/SHIELD MITIGATION (50% Physical Reduction)
Initial Damage = .5 * 2252 = 1126 Damage
Shadow Damage = 1126*.75 = 844.5
Total Hit = 1713.48 (Factoring In Resilience)
Crit Damage = 1713.48*2.3/1.25 = 3152.8 Damage
Delta Hit: -696.52
Delta Crit: -1282.2
MAIL MITIGATION (40% Physical Reduction)
Initial Damage = .6 * 2252 = 1351.2 Damage
Shadow Damage = 1351.2*.75 = 1013.4
Total Hit = 2364.6 (Factoring In Resilience)
Crit Damage = 1713.48*2.3/1.25 = 4350.86 Damage
Delta Hit: -45.4
Delta Crit: 84.136
LEATHER MITGATION (30% Physical Reduction)
Initial Damage = .7*2252 = 1576.4
Shadow Damage = 1576.4*.75 = 1182.3 Damage
Total Hit = 2398.7/1.15
Crit Damage = 4413.92
Delta Hit
Delta Crit
CLOTH MITIGATION (20% MITIGATION)
Initial Damage = .8*2252 = 1801.6
Shadow Damage = 1351.2
Total Hit 2741.57
Crit Damage = 5044.48
Delta hit = +331.57
Delta Crit = +609.48
Please take this into consideration Devs. There are for more ways to make the ability more interesting that could be made in conjunction with this change or in conjunction with the current Scourge Strike.
Someone please cross post this in the Damage Dealing and Test Realm forums.