Kal El could decide if he wanted to save the Kriptonians or not, he can decide if he want children or not, he can decide by himself if he wants to be Kriptonian or human or both, still he had a decision.
Zod learn to fly, because he is train to master this things in second, this is to show his militar nature against Superman nature of a farmboy, who fail at control this the first time he use it.
Seriously, from all the flaws movies hev you pick something like thi, there is aliens that can destroy buildings with one hit and this is unreallistic?
Avengers show you an alien invasion too, no one died, the alien never try to destroy any building and everybody survives, how in hell this could happen?, no consequences to their actions, without consequences there is no point in making things.
Its more unreallistic that any type of invasion cause no damage to the street and human life, here you can notice Zod wa triying to cause as much damage as posible, Zod knew how to fight, Superman dont so he could make this destruction in a fight because he was in control of the fight.
There was one survivor easter egg in the movie, one of the scape pod is empty, what other Kriptonian survivor we know and is part of the house of El?
She was the only connection they have to him, also they need information about humans, is not so hard to notice they where looking for something in her, also they knew about the ship in some way, as far we know it wasnt from Kal El mind.
Superman has killed Zod, i think he actually killed him twice in the comics, also Zod wanted to die, he lost all his mission on life, he had no destiny and reason to live, he cant kill Clark since he is all Kripton now, so he cant actually kill him or keep living, was a suicide by cop.
He mean about adapting in the human society, not in the nature, also Zod is design as a warrior race, the fact the air did little to them is because they are design to be harder and survive.
Superman is an alien, what the hell you think mankind is going to do to an alien?, fear him and like everything mankind fear, it will try to destroy it, Johnathan Kent was acting like a father, if your father dont care the goverment open you so they can see your organs, study you as a rat and those thing, your father sucks as father.
Because they changed status quo it means it suck, news flash Super heroes are about changing status quo.
As much as i wanted this, is time to let him go and move with our lives.
I know whew all this nostlagia i coming, i love him too and i cant belive he is gone, no one else in my heart is going to be Superman but him, but i dont let nostalgia blind me.
Because that what people wanted, becuse it would mean he is still here, but is time to let him go.