Who cares if Blizzard’s writers think it was a mistake or not? It’s a plot hole they wrote into existence when they retconned there Eredari of Warcraft 3 to be related to the Broken.
Even if there are no NPC’s that recognize it, the Draenei had thousands of years that they could have been forging diplomatic ties with the Orcs and other races of Draenor. In that time they could have been fortifying them against the Legion and their deceit. Instead they chose to live in seclusion and keep their knowledge guarded from all outsiders.
Even if the Draenei were to argue that it was not a mistake to do so, it’s obvious that it was given it led to them being distrusted and feared by the Orcs which just made the Legions job of turning them against them all the easier.
Unless you want to argue their big mistake was when Velen helped Durotan. I don’t think that would have slowed Guldan much though.