Demon Hunter

Demon Hunters are the second playable Hero Class added to the game. Added in Legion pre-patch Blizzard decided it was too much work to create and balance 3 new specs so demon hunters were only given two specs: Havoc and Vengeance- a dps and tank specialization respectively. The addition of this class brought all of the Illidan fanboys out of the rafters to create a million demon hunters with names such as: Illidansgame, Illidamgurl, Illidanny, Skillidan, and basically any other shitty Illidan pun you can conceive.

Havoc

Havoc was introduced as a high mobility spec that basically had all the movement benefits of the monk class but without the complicated dps rotations. Havoc DHs used fury as their resource which was generated from spamming demon's bite or taking the demon blades talent that removed demon's bite and added a chance to generate fury with every auto-attack. Fury generation was basically clunky and shitty for the entire expansion unless you were lucky enough to get The One Ring as one of your first few legendaries before quitting the class. Since the ring was basically required to do damage they built the tier bonuses around fury generation and nerfed the ring every patch to try and even out the playing field for shitty havoc demon hunters (ones without the ring).

Since the balance team tried to fix havoc using the tier sets they were forced to play with whatever set of talents that best synergized with the current tier set or do sub-par damage. The first cookie cutter build was the momentum/bloodlet build that made your only ranged attack your main source of damage by adding a bleed effect that almost tripled the damage of the ability. This spec was popular because throw glaive didn't take any fury which was very convenient because fury generation sucked ass as a fresh level 110. This spec stacked crit and versatility since throw glaive was physical damage and received no bonus from mastery and there weren't really any haste breakpoints that provided a real damage boost.

With the release of the Trial of Valor and Nighthold came Legion's first set of tier bonuses that slightly increased fury generation across the board and saw a lot of demon hunters switch into the demon blades talent. This talent made fury generation a passive endeavour which (if you were lucky with your generation) opened up more GCDs for actual damage abilities and not just spamming demon's bite for fury generation. During this time a lot of people (especially if you had the ring) switched to the cooldown stacking spec because there was actually enough fury generation to do some attacks instead of sitting on your hands for 5-10 seconds at a time waiting to gain some fury.

Tomb of Sargeras release brought the second set of tier bonuses and first blood became the talent of choice for everyone since the tier bonus incentivized you to use it on cooldown to get some refunded fury. Now without bloodlet versatility was a shitty stat and DHs started to search out some more haste for increased autoattacks and fury generation. This further led to the rise of the cooldown stacking builds (and the death of the momentum talent thankfully) using meta, chaos blades, and nemesis to do a staggering amount of damage in a 30 second window and then proceed to be useless for the next 90 seconds.

Once the second set of legion legendaries was added people realized that you could further benefit from cooldown stacking by using the Delusions of Grandeur and two meta cooldown relics to reduce the cooldown of meta to near two minutes such that you could stack the use of all your cooldowns every two minutes instead of an alternating 2/4 minute rotation resulting in a big boost in dps. Provided you had both the ring, shoulders and 2 meta cd relics this was an attractive option from nighthold onwards to the end of the expansion.

With Antorus and the final set of tier bonuses came the nightmare every demonhunter was dreading. The memespec. To effectively leverage the tier bonus that gave a fuckton of haste after using eyebeam Havoc players switched to the "Demonic" spec which gave you a short "mini" meta every time you casted eyebeam. This spec also used a new method of fury generation using Blind Fury and Demonic appetite which gave you a bunch of fury while casting eyebeam and allowed you to cleave small purple balls from the enemy you were attacking that spawned randomly on the floor around you. Picking up these purple balls gave you a chunk of fury that allowed you to keep spamming your damage dealing ability. At the end of the day this spec amounted to one running around like an idiot trying to pick up all the purple balls so you could keep doing damage while trying to disguise the reasons you died to mechanics such as standing on tanks or loitering in the fire.

Vengeance

Vengeance sucked ass. Basically a blood DK that traded in it's ability to not suck for the ability to jump around the room trying to stay alive while their tits got ploughed. They use pain as their main resource for threat generation and mitigation which was essentially limited to some self healing and a parry buff that had ~50% uptime. Veng DHs basically took tons of damage all the time and were pretty much useless as raid tanks from the get-go.