So I've been going through half the classes/specs legendaries and I see some glaring differences in usefulness.
Feral Druid example
Ring - Increase energy by 100
Boots - Predatory swiftness stacks up to 3x and gain 1 stack every 15 secs.
Gloves - Crit from bleeds have 40% chance to trigger primal fury
Wrist - Increase thrash damage by 25% and radius to 25%
Our best legendary is what?
Eye of the Twisting Nether - Dealing damage with Fire, Frost or Nature abilities grants separate, stacking 2% damage increase buffs. Much like the bracers, this heavily encourages taking Hailstorm as you will be maintaining your Frostbrand effect to get all 3 buffs. Bear in mind all 3 applications are separate and will need to be managed on their own. Is the best single target option, and also the most versatile choice, making it the Legendary of choice for most content.
so a 6% damage increase when you go through your rotation.
Emalon's Charged Core - 30% increased lava lash damage when frostbrand/flametongue are active is a joke. When it was 60% because it was 60% was the only reason it was reasonable to use this legendary and skill. How the hell often does anyone lava lash anyway compared to their other skills?
Nothing else is worth mentioning they are AE dependant or are some generic health buff that every class gets.
On a fight like Nyth in EN lava lash accounts for 2.34% of our damage, 30% increase on something that accounts for that much damage now is ridiculous. We have trinkets that perform 400% better than lava lash and we don't even have to cast the bloody trinket not to mention our gold trait unleash doom but let's not even get into doom vortex.
Our 4p set makes our lava lash give us a 20% chance to proc stormbringer, something that we use 16x on a boss fight compared to 100x casts on stormstrike with a practically stationary target. Let down or what? Hell do people even use lava lash any other time except in a dungeon? so the 4p is useless outside of anything that doesn't live longer than a minute.