TBH the OP is not wrong, but the Blizz writing is to blame.
Blizzard decided to make Yrel evil in service of a brief Maghar recruitment quest line. Also they decided to make the maghar more sympathetic after everyone fought against them for the entire WoD expansion.
I think that the maghar should have been recruited from Outland instead of AU Draenor. It could have involved a questline searching for Thrall across Outland and finally finding him in Nagrand. Would have made the cinematic with him and Saurfang less abrupt and random. It could have also involved a trip to Garadar and a reflection on how things went so wrong with Garrosh. I think that would have been neat.
Your argument is perfect and without flaw. Of course the Draenei caused all that death and destruction! If they would have simply laid down and let the Legion kill them the Legion would have sat home and never left! Thus saving the universe!
Watch all the Slyvanas loyalists list how Yrel is so even, despite we only just saw her for five sides from the Horde side, saying how evil is she! Let’s kill them all. All while sitting on a throne of thorns and spikes, because Slyvanas is just as evil for committing genocide. Watch them say Yrel committed genocide, and Slyvanas didn’t, despite they both are bad.
Hey. Hey! Tripple up all the wages and set up a decent union and kick out the irradiated trogg huggers and you can have the finest planetwreckers on yourside too!
Hey now, don’t stray from your flawless argument. Already backing out? Of course they had to lay down, it’s the only way. Let’s not go back to your boomer ways now.
The Draenei didn’t go to Draenor because they wanted to, their ship broke and they crashed.
And there is a deeper reflection behind it.
Void was already dominating the planet, by the way, the twilight hammer was born there. Cho’gall was already making moves towards the entrance of Void. If the Draenei were not there, the entire planet would be lost.
And consequently the Orcs would not go to Azeroth, and consequently the Legion would have won the 3rd War.