IDK if this stuff was in the book, but I didn't get that from the movie. Bean and the Indian kid were smaller, and so was the big nosed team captain. As for the stresses to which he was subjected, that is a common aspect of elite military training, and adds a degree of realism to the somewhat implausible premise of kids commanding fleets in a real war. They were looking for the one guy who was to lead their fleet to victory - not testing him within an inch of his life would be just a bit irresponsible.

The point is to foreshadow his final tactic. Duh.
If there is anything moralistic going on, I'd call this an analogy about what we do to soldiers. We send them blindly out to kill people we say are the enemy, we narrow their focus on a simple task at hand, and cause them to commit horrors and atrocities without necessarily getting to contemplate the ramifications of pushing the buttons and pulling the triggers. I doubt the crew of the Enola Gay was fully briefed on the implications of what they were ordered to do.

I read Ender's Game years ago, but I recall it as a short story or novella, which ended with the revelation that what he thought was a game was actually the war, without any of the family stuff or making friends with an alien. From that, I got the impression it was a gimmick story aimed at just the surprise reveal.

Well, he's not a Mary Sue. A Mary Sue wouldn't have his emotional distance or the difficulties he encounters at first before working them out.
That's not an extraordinary amount of violence. That's just life. I don't know how much experience you have in all-male environments, teams or stress situations, but Ender got off easier than lots of kids do where bullying is concerned.
OMG!! A sci-fi story with an anti-authoritarian message! What next? Card is REALLY unique! This must be some deep-seated revelation about his character and personality that he would choose to write a sci-fi military story that portrays authority in a negative light! I mean, who else would dare such a thing.

Or maybe if someone had more masculine experiences and entertainment than My Little Pony prior to watching this film, it would not have had such an impression.

Well, there is the whole "don't trust authority, because they will use you for their own purposes, regardless of your intentions" message...

Anyway, the issue I had with the movie was that they made such a big deal of Ender's empathy and ability to identify with his opponents, and that had nothing to do with his tactics or success. I mean, how much empathy do you need to come to the conclusion that the enemy will not like having his home planet blown up?

And what sort of unique insight into the enemy's thought process was required to dredge up a rehash of the same tactic he had previously used to win one of their training competitions? One could argue that Ender is not some brilliant military commander after all, he is simply the one who best fit into the slot that was predetermined by the training program. The emphasis of the zero-g obstacle course laser tag geared the student's minds to work the problem of getting a single unit to a particular position. Just about zero real life battles have been won in that manner, and it only succeeds in science-fiction because the authors invent enemies who can be defeated in such a manner.

Whatever else Card was saying about war or the military (and I would bet that not only is my interpretation widely accepted, it is the reason for the long-time popularity of the work; just like all the hippies who thought the One Ring of Tolkien was a metaphor for nuclear arms, that same breed of leftist counter-culture sci-fi fan jumped all over this one), he dropped the ball when it came to telling an airtight story.