Casual Raiders Suffer.

No matter what Blizzard says, making new raid tiers undoable by pugs is total garbage. Personally I have absolutely no problem doing older raids, but seriously is making the first 2 or 3 or maybe 4 bosses of a new raid easy all that much to ask?

We actually do have a measurement of sorts in place like this. It might not be to your expectations if you want to successfully pug half of the bosses during the first week they're available, but it's worth mentioning it does exist.

Whenever designing a new raid dungeon, we have a basic 1-5 scale we use to rate each encounter in terms of complexity. While complexity may not be synonymous with difficulty in some cases, it is in most. So for an example of what we're looking at, every encounter in Molten Core would be a 1 on our scale in terms of complexity, while bosses like Cho'gall and Sinestra are each considered a 5. (For an example of when a complex fight might not translate into difficulty once the mechanics are known by the raid, Flame Leviathan is also a 5 -- there are a LOT of mechanics in that fight.)

So, using those few examples, I'll say we try to create the raids of today with the average complexity of all boss encounters dialed in around 2.5. We have to balance out the really complex encounters with encounters which have more simplistic mechanics. Again though, that doesn't always mean they're less difficult.

To define complexity, we're talking about all of the spells, abilities, scripts, or mechanics triggered during each fight. So if you look at a boss like Lucifron (1) in Molten Core, there are fewer than 5 mechanics in the whole fight. Meanwhile, Beth'tilac (5) in the Firelands has well over 100 mechanics (not just spells and abilities, but triggers for webs, adds, etc.).