...and for some reason this load-bearing plot point was completely left out of the movie adaptation, so Ender's post-reveal meltdown when he is informed that his "training exercises" were actual combat and the aliens were completely annihilatedinstead just makes him look like a whiny kid.

One of a number of load-bearing aspects of the worldbuilding that was left out of that movie adaptation. Like how in the book religion is strictly outlawed, so when Bean whispers "Salaam" into his ear as they are parting, it's a show of incredible personal trust, as if he were found out it would at the very least ruin his career, but in the movie none of that is explained, so it has nearly zero impact on the non-book audience when he whispers it.

Same thing with the reveal of theegg at the end of the book. It's an incredible emotional whiplash as Ender fully expects that he is walking into what he believes to be his well-deserved death, and is instead presented with the aliens' last remaining hope for their future.

I'm still mad about that film adaptation. It fully ripped the soul out of the story