Blizzard is making a ton of adjustments to numbers in WOW in their upcoming patch. Mostly I agree with their direction, though I admit I do question how they got some things so wrong in the first place. Legendary items have been a real point of contention for the whole expansion so far, most especially because there has been such a monstrous difference in power level between them.
Some Legendaries were really godawful. For example, Prydaz was a Legendary neck common to all classes and it was horrific. It granted 15% of your health as a shield if you didn't take damage for 5 seconds. On many fights this would never happen, and it usually meant that the shield happened at the worst possible time. Best case this item is 2% of a healer's output, worse case it is nothing.
On the other hand we have good Legendaries that boost output directly. The most absurd of these gave up to a 20% damage bonus, which is completely out of line. The ones I could have gotten as a ret paladin were more like 7%, which is really powerful, but not quite as absurd. Those numbers are simply too big. Getting garbage Legendaries and being 15% behind other people means you are practically losing an entire tier of power. Also if you have a single item doing 20%, what possible utility item could keep up? Are you going to give someone 100% bonus movement speed? Invulnerability? These are the kinds of benefits you would need to toss around to compete, and they would obviously destroy encounters.
The new standard seems to be Legendaries that do 4-5% bonus damage. This is still powerful, but since Blizzard is intent on offering a variety of Legendaries that do this much damage nearly everyone will be able to have something good to use. Both of the damage boosting Legendaries for ret paladins are being nerfed such that they are in this range, which doesn't affect me since I had neither of them. I think 5% is a reasonable target. It is big enough that you notice it in your dps numbers, relevant enough to mix up your rotation for, but you could offer utility that is a reasonable choice against it. For example, I have boots that give me 16% movement speed. That is a lot, and although it will rarely be worth it from a raw damage perspective, it will make dodging bad stuff a lot easier and that has value. If I were running towards my target for 20% of the fight it would even be as much of a damage boost as a raw damage item.
There is a real balancing act here. You want damage dealing Legendaries to be noticeable. If they are 1% boosts then the benefit will be lost in normal variation and it won't be enough to actually impact the way people play. At 20% they are mandatory and if you don't have them you are worthless for challenging content. 5% is the right point where you can see the difference, get excited about it, but not be a whole new character.
I suspect everyone is still going to be all about the damage Legendaries rather than utility. However, the newest numbers on the utility items seem reasonable - the Prydaz example I mentioned earlier now heals for about 8% of a healer's output regardless of raid conditions. That is good enough that you would really notice it, and you might even get your whole raid to wear them, drop a healer, and end up ahead. I am not at all convinced people will do this, but since it actually seems like it might have advantages people shouldn't be too disappointed in defensive options like this.
On my last Xavius and Cenarius heroic kills if I had used the new Prydaz it would have prevented fully half of the damage I took during the fights. That is serious healing and should not be ignored. Of course people will ignore it because they want to dominate damage meters, but it *shouldn't* be ignored.
Blizzard is currently aiming for a sweet spot that I approve of. Whether they will hit it with all the items is another question entirely. At least they have a plan though, and it seems reasonably consistent, so that is a good start.