I feel like there’s a lot of nuance here missed. Genn was tipped off by Detheroc who was disguised as Shaw. “Shaw” was also likely keeping secrets from Anduin.
Do you even know Detheroc was posing as Shaw at the start of BFA? Do you know he was the one pushing the Alliance to war with the Horde?
Ya’ll were duped by dreadlords. Everything you are arguing about is irrelevant in context.
That’s not true, play the game
Not at all.
Andiun learned that the Horde did not murder his dad much later in BtS.
Andiun just didnt want to have two front war but gave Genn full authority to make decisions.
https://wowpedia.fandom.com/wiki/Detheroc#Legion
As Shaw, Detheroc spoke lies to Anduin Wrynn about the Horde and manipulated the new king into preparing Stormwind’s armies to attack them, intent on instigating another conflict between the Alliance and Horde when the world could least afford it. … [13]
^ N Rogue [45] A Simple Plan
Detheroc spoke to Anduin, not Genn.
Anduin didn’t buy it.
the whole Broken Shore attack failed because the dreadlords orchestrated every pivotal moment. Including the apparent Horde betrayal that caused the death of Varian.
Genn is literally saying inthe Cinematic “I knew we couldn’t trust her”
The Alliance was under the impression they were betrayed by the Horde in a joint attack.
Yes. And that means Anduin was aware of what Genn thought and still ordered him not to cause trouble unless he caught Sylvanas doing anything.
He did not catch Sylvanas doing anything.
He left with the intention of killing Sylvanas and the Horde the very moment he could encounter them.
And apparently convinced the Alliance not to take five minutes to ask the Horde why they retreated during an important operation.
Like the most ridiculous contrivance in Legion was no one clearing this point up immediately afterward.
So what? This doesn’t change the fact of the premise.
The Alliance is still under the impression that the Horde struck the first blow by betraying them to the Legion and getting Varian killed through treachery.
Andiun just told them “Don’t fight the Horde if you don’t have to” but at the end Genn had command and he commanded an attack because of a perceived Horde action.
This premise holds true. You can keep complaining about Genn not obeying every god emperor andiun’s words to the letter but this doesn’t change the fact that:
The Horde was framed for getting Varian killed and the Alliance responded in Stormheim.
Good luck doing that with the Dreadlords infiltrating the Alliance intelligence network and trying… almost succeeding in starting a faction war in Legion. Thankfully the Rogues campaign hall stopped it.
Legion had some fun retcons but we have to respect them for the effort they put into it.
This little issue is properly explained.
Within the bounds of the story presented, sure it is explained. But it’s not like Anduin couldn’t go to Dalaran at any point to ask Khadgar or something, there were possibilities that didn’t involve controlled correspondence.
It’s the reason I’m calling it a contrivance rather then a plot hole. It’s acceptable, I just don’t see it as extremely compelling.
He could have messaged Baine, they were still buddies. They roll out Anduin and Baine’s friendship just to undermine the Horde, and not the Alliance it seems.
And there is a million other contrived reasons why he couldn’t.
Like Dalaran being unsafe, or Andiun might get assassinated by the Banshee or even the Legion being responsible.
Its a grey area, there is End Times war on with shapeshifter demons who have had thousands of years to master suberfuge and sabotage.
Its a cluster F of a mess.
Its acceptable as reasons go and by wow’s story telling quality levels this is the gold standard.
If you want a contrived, unconvincing mess lets look at BFA and Shadowlands.
Dreadlords could shapeshift to Baine/Andiun, mislay the actual location. They could assassinate either Baine or Andiun while they are traveling.
Legion really was the greatest expansion ever. We rose too high… the only way left was down.
Legion was also the most misleading expac ever…
Horde and Alliance working together? Next expac, genocide wars
Heroic Sylvanas? Next expac, You are all nothing!
Dead in the Emerald Dream? No no, you’re actually in Ardenweald and going to die forever
Krokul master race? Nah, take these yellow eyed draenei instead.
I hate playing through Legion now because I know what comes next.
Those are all BFA and Shadowlands points
Not initially anyway. He just happened on sylvanas binding a Angel for more power. And he wasn’t hunting the horde, but Genn does say he’s going to find a reason to attack Sylvanas. He just conviently got what he was looking for in the end.
That cinematic alone really did a lot to show off how cool Genn is….In my opinion 
It is not complaining to simply state the fact. What is it with you people?
Anduin himself gave Genn a stern rebuke for Stormheim in BtS. The Alliance provocation at Stormheim was not fair play. It was an example of the Alliance’s inability to control its chain of command.
Which is why The War of Thorns was such a good sell to Saurfang. He thought about the Horde being attacked by the Alliance there. That there were no consequences he was aware of - because Anduin did a private rebuke.
Genn’s actions led to the War of Thorns and the Burning of Teldrassil, because Genn gave Saurfang good cause to go to war.
I am not complaining. Just stating the facts. I thank the Goblins for making the catapults more powerful than ever before! And the Troll Mages who lit the flames. And the Troll Shaman who made everything extra crispy.
no sorry, Micah. The Skyfire attacks the Forsaken fleet in Stormhiem in a sneak attack. The Forsaken ships were just anchored, they were not doing anything to jutify the attack.
The Alliance struck first.
Gee, I wonder which group attacked Gilneas, blighted it and was responsible for the death of his son…. 
I’d bomb the forsaken too if I was him.
And then the Horde would burn down which ever tree house you couch surf in.
Alliance provocation after a perceived attack at the Broken Shore.
Why does Andiun need to tell Genn not to go for it unless necessary if the Horde and Alliance were not at high alert against each other.
There is no logic in that statement unless the Alliance viewed hostility between the Horde and themselves as likely.
Oh please it was a contrived mess from beginning to end.
How many times has the Horde attacked the Alliance with zero public rebukes?
Sylvanas’ plan to feed the souls to jailer led to the War of Thorns and Burning of Teldrassil.
You are not complaining no, you are just doing revisionist lore to somehow explain the inexplicable in BFA.
In Azsuna there are worgen gathering intel from a sunken forsaken ship which helped them find out what Sylvanas was after, in fact they send you off to Genn to share the news. In the Horde version of the quest the Forsaken thank you for saving them the trouble of having this info falling into the wrong hands.
Before BFA launched Blizzard decided to make the zones be availble in any order but these quests still exist and are there in the game.
Well, since the forsaken can’t win in a fair fight, of course they’re going to rely on their handicap.