For anyone who's been playing WoW at all in Legion, you have surely heard, if not experienced first hand, the huge disparity caused by the horrible implentation of Legendary gear. Having a random chance to get either a Legendary that provides a huge mechanical boost to your spec, or, a seldom used utility buff has left many completely frustrated, or having to play alts that they don't really care about, only because that alt got lucky with Legendary drops. I believe that topic has been covered in plenty of depth. The Developers know, at this point, what a terrible design flaw they added to the game, and have talked about how they want to fix it in future expansions: primarily by only having utility legendary actions, rather than some utility and some DPS/rotational legendary actions.
However, there's another aspect of the implentation of Legendaries in Legion that is only now becoming a really significant problem, and will unfortunately be getting worse the further we get into the expansion.
A Tale of Two Hunters
Let's imagine a raid team with a couple hunters in it. They've worked their way through a fair number of m+ dungeons to get their weapons upgraded, done a couple weeks of both normal and heroic Nighthold raiding, and are getting ready to start mythic progression. Both of these hunters are 890 ilvl, and have similar trinkets, both have their 4 piece set bonuses. And, both have two legendaries. I imagine this is a fairly common situation. The only significant difference in these two hunters, is one has gotten Legendary drops for armor, and the other only for jewelry.
Let's call the hunter with legendary armor Halduron, and the hunter with legendary jewelry Loren. Their stats then look like this:
Halduron then ends up with 12.2% more Agility than Loren. You might expect, with the larger than average secondary stat budgets that rings and necklaces have, that Loren would have significantly more secondary stats to make up for it, but instead, we see he only has 5.9% more secondary stats than Halduron.
Again, you might think that Halduron must have tons of gem slots, making boosting his secondary stats, but in the actual two hunters I took these stats from, Loren has 6 gem slots, while Halduron only has 3. So the actual disparity of secondary stats would be even larger if they had the same number.
Progressive Stat Scaling in Legion
Over a year ago, Celesatlon announced that they were changing the way stat scaling would work on gear over the course of an expansion. Traditionally, the stat budgets of higher ilvl gear had increased exponentially, so you had nearly double the stats on your gear every tier (perhaps not exactly that much, but close to). However, that meant by the end of the expansion, it was common to have huge amounts of your favorite stat, which apparently made the game extra difficult to balance.
However, they recognized that some specs were nearly unplayable until you got to a certain amount of a particular stat. So they decided to leave in the exponential stat budget scaling up through heroic dungeons or "raid ready" gear.
Finally, to ensure we'd keep feeling more powerful, they decided to leave the stat budge for our primary stat scaling exponentially, and only reduce the scaling to linearly for the secondary stats.
It's worth noting also that all of the legendary jewelry has two stats, so even if there are specs out there (maybe arms warriors are closest?) that have a secondary stat that's close to twice as valuable as their primary stat, not all of the secondary stat budget will be used on that one amazing stat.
The Tomb of Sargeras and Argus
Going forward, this effect will be much, much more pronounced. If the goal of having different scaling rates for gear stat budgets was that eventually, ilvl will be the only important aspect of armor, then it seems they've come up with a decent solution. But it leaves a huge problem for those of us who can't get any legendaries to drop other than jewelry.
Assuming that Blizzard isn't willing to fix the problem until a new expansion is released, hopefully they're willing to add something to the game which will allow those players with the worst of luck to swap out their less-than-legendaries for actually legendary Legendaries.