When Grom started fighting against Gul’dan, he did so alongside us and Yrel. Text in the quest itself from people who lived through the event tells us that the Magh’har and Draenei went on to then expel the Legion together. It wasn’t until after the Legion was done for that the Draenei turned their attention elsewhere.
https://wowpedia.fandom.com/wiki/Bonds_Forged_Through_Battle
We know the events of BfA take place some 30+ years after WoD because we’re told that when the Bronze Dragon Kairozdormu took Garrosh to Draenor the first time, he didn’t just go to Draenor, they went into the past. This is explained in the Warcrimes novel (don’t have a direct quote, but references to it if you want) and is why the trailer for WoD opens with “35 Years ago”.
However, when the Horde player returns to Draenor in the events of BfA, they do not go through by the same means and do not travel back in time. Grommash has an adult child compared to when he had no children in WoD. Gey’rah, who wasn’t even born as of WoD–as her mother Drakka was pregnant for the first time–is now well and truly an adult. We’re in a contemporary Draenor, some 30 years after the events of WoD.
https://wowpedia.fandom.com/wiki/Hero_of_the_Mag%27har
https://wowpedia.fandom.com/wiki/Geya%27rah
This new generation has been fighting the Legion alongside the Draenei until, as explained in the first link, the Draenei turned on them. They don’t mention anything about wanting to stop the Iron Horde, which has been gone for decades. Yrel and Grommash have since become closer, so in her eyes he has made amends for his past crimes.
This is not a case of the Lightborn forces simply acting in self defense. They are the aggressors in this scenario. They are conquering/slaughtering other races of Draenor–not to stop tyrants–but out of their own religiously fueled apocalyptical beliefs.
https://wowpedia.fandom.com/wiki/Tyranny_of_the_Light
There is evidence of mind control in the fact that Xe’ra’s Lightforging can transmogrify someone, altering not just their physical body. And the constant references to zealotry, fanatacism and But no, no examples of her just puppeting people around.
I’m not saying she is being mind controlled. Merely that being under superntural influence as a result of having her body/mind altered by Lightbinding/forging or purposefully mislead/manipulated by would be an out.
I don’t think Yrel was the best candidate either. I think Blizzard would have been better off using someone who actually lives on Azeroth, who is an established figure in the Church of the Holy Light, and isn’t acting under the influence of some big bad supernatural force. You know, give the Alliance and Light as practiced on Azeroth some more nuance.
I’m pretty sure that the decision to go with Yrel–who isn’t even a member of the Alliance and exists in a alternate universe–and possibly Turalyon–who hasn’t been a member of the Alliance for decades and has spent that time hanging out in parallel universes–is due to Blizzard’s general tendency over the years to distance the Alliance and its major characters as much as possible from anything that would tarnish their image as being squeaky clean/always on the right side/justified at all times.
But Light based antagonists, and even outright villains, have always been a thing in WoW. I can’t agree that the concept makes for a bad story.