On the official WoW Rogue Discussion forum, Palaelf asked,
Why no changes for combat rogues? Us combat rogue stuck it up with a boring spec to play with in Arenas how about something nice for us? All I see is changes to Sub and Mutilate trees and the only thing I see so far for Combat Rogues is a NERF with this new "Expertise" rating how will Arena rogues keep a proper hit rating? We already miss a ton in a full arena gear set. Now we are going to be missing our sinister strikes making us a shiv only class?Drysc replied,
Nope. No changes. We're not required to make changes to every class or every tree just because other trees may see changes. Have you tested or even thought about the dps increase of actually being able to stop your target from dodge/parry with the expertise rating? I'm going to guess not.
So, how good or bad is Expertise going to be for Rogues? I guess that depends on a lot of factors.
Currently, it is widely acknowledged that +Weapon Skill is most useful when fighting against level 73 NPCs, aka boss mobs. Weapon Skill has a unique mechanic in that once a mob's Defense exceeds your Weapon Skill by 11 points or more, your Miss chance is increased by an extra 2.5%, rather than just an extra 0.5% to Miss. Thus, a level 73 mob has 365 Defense and players have a natural maximum Weapon Skill of 350. 5 points of Weapon Skill are enough to eliminate this 2.5% advantage. 5 points of Weapon skill is also enough to improve your to Miss chance against any mob by 0.5%. So, if you have 355 Weapon Skill versus a level 73 mob with 365 defense, you have given yourself a 3% bonus to hit versus the mob.
At level 70, 3.9 points of Weapon Skill Rating are required to increase your actual Weapon Skill by 1. However, in Patch 2.3, all Weapon Skill bonuses will be converted Expertise. Expertise Rating will convert at the same rate as Weapon Skill rating.
So, what exactly is Expertise then? A totally separate mechanic from Weapon Skill. In fact, after patch 2.3, there doesn't appear to be a way to increase your Weapon Skill except waiting for level 71 when Wrath of the Lich King is released. Every piece of gear, every talent, every racial abililty that affected Weapon Skill has been removed. Racial abilities have been converted to +Crit. Talents have converted to Expertise and gear from specific weapon skill rating to an expertise rating.
For each point of Expertise, you eliminate 0.25% of your target's Parry and 0.25% of your target's Dodge. Where does the eliminated Parry and Dodge go? Straight into the ordinary hit part of your attack table. I'm not going to go into an entire discussion of the attack table, but I do suggest you read up on it on WoWWiki if you are not familiar with what I am talking about.
So, while 5 points of Weapon Skill eliminates 3% of the Miss chance on Level 73 target, 5 points of Expertise will eliminates 1.25% of your target's Parry and Dodge for a total of 2.5% to hit. This may be very disappointing to some tanks. However, Expertise scales much more quickly than Weapon Skill. 6 points of Expertise gives a total of 3% to hit and the 7th points of Expertise gives a total of 3.5% to hit. You need 10 points of Weapon Skill to eliminate 3.5% Miss Chance on a Level 73 target. 10 points of Expertise is going to eliminate 2.5% Parry and 2.5% Dodge from your target. Would you rather than a 5% better chance to hit your target or a 3.5% chance.
You might have noticed I keep using Weapon Skill against a Level 73 target. That's because that's where you get the most benefit. On a level 60-72 target, each point of Weapon Skill above 350 merely gives you a 0.10% reduction to miss your target. So, if you have 355 Weapon Skill, you have a 0.5% better chance to hit your target. 365 Weapon Skill only gives you a 1.5% better chance to hit your target. Compare this with Weapon Expertise which gives you a 0.25% reduction to your target's Parry and Dodge, so 0.50% reduction per point. At 15 points of Expertise, you'll reduce your opponent's Parry and Dodge by 3.75% each, or 7.5% total, regardless of their level.
However, Rogues and other melee DPS fight from behind their targets if possible. We do it to avoid nasty Cleaves, but also because when you attack an NPC target from behind, they are denied their Parry. Thus for Rogues, half of the benefit for Expertise is negated by this mechanic. Against Level 73 targets, 10 more points of Weapon Skill from Weapon Expertise gave Rogues 3.5% to hit. After Patch 2.3, Weapon Expertise will grant 10 points of Expertise attack ing from behind will give Rogues a 2.5% chance to hit.
Lastly, players do not get a chance to dodge attacks from behind. So, in PvP, if you are focusing on attacking another player from behind, you will gain no benefit from Weapon Expertise as they cannot parry or dodge.
Overall, this may eventually help Rogues. We'll do more damage against trash mobs and we won't always be behind our PvP opponents. There have been some extensive testing posted on the Elitist Jerks boards, but I still think the verdict is out on whether Expertise will be better than Weapon Skill.