There are some changes coming to Diablo 3's metagame, and they are ones I heartily approve of. I mentioned awhile ago that the far and away dominant strategy of the endgame is to leverage a single wizard build using Energy Twister for damage dealing with all other characters being pure support. The wizard group damage build is so far above all other characters in terms of damage potential that there is no other viable option at all. Clearly balance will never be perfect and the top players will gravitate towards the theoretical best builds, but in this case the difference was too stark. For example, I found that my best damage build for the Witch Doctor was doing at best 10% of the damage of an Energy Twister wizard with a proper group, and no endgame damage build should be that far ahead of the pack.
The reason Energy Twister was so outrageous was that the damage scaled by the square of resource input. Casting twice as many Energy Twisters multiplied damage by four, and wizards could ramp up their resource generation through using health globes, so every group included two characters focusing entirely on buffs and producing enormous quantities of health globes. Blizzard has put up massive nerfs to these health globe generating effects, and for good reason.
Here is the real problem as I see it: Basic good builds should do something. If I have a really powerful soloing build I shouldn't be completely irrelevant in a group. Certainly tinkering with the build to add in more group buffs or utility makes sense, but if a group is doing four person content and someone says "Hey, can I bring a top tier soloing build along?" the answer should not be "Uh, no, you will be totally useless." A good build should be better than idling in town, but this isn't really the case at the moment.
I feel like this is a similar stance to how I like my roleplaying games balanced. If someone makes reasonable decisions like "I will play a fighter, have high strength, use a sword, and bash people." then they should contribute fine. The game shouldn't be set up so that such a character is totally worthless compared to the melee character with 4 classes who stacks Charisma because they can add it to their attacks, damage, saving throws twice, and AC via a complicated series of feats, gear, and class features. Similarly I want good soloing characters to be worse in groups than dedicated group builds, but they shouldn't be a joke.
In roleplaying games I like the balance to be a lot tighter, so that optimized characters are perhaps 25% better than reasonable characters. You can build a terrible character any number of ways, and that is just fine and not something that worries me. In D3 of course optimization is often an order of magnitude in difference, so everyone being within 25% of each other isn't really feasible - unless you spent years without introducing new stuff you would never arrive at that magic point. However, they can definitely do better than they are doing right now, and it looks like the next season is headed in a good place.
Until they create a new item that starts some ridiculously overpowered build next time. It will happen, we know it will happen, we just don't know which item or which build yet. Such is the nature of content churn.