"Superman is an immigrant story" is a nice talking point but has never actually been true in like…any medium.
Sure he comes from a faraway place and now resides in America, and yes you can use that to say something about immigrants, but nothing about Superman otherwise fits.
He has no memory of his ancestral home because it was destroyed AND they deserved it. Superman never faced anything resembling what immigrants face in the real world. He's benefited from being a white man all his life and has blind spots because of it.
What Superman is actually about is power and the fantasy of Superman is that we actually have the "right" person with that power.
Yeah I don't really get the idea that Superman is meant to be an immigrant. That's a Martian Manhunter story. Superman's always been coded as a nerdy white guy. It wasn't really until recently that people have emphasised his alien origins.
The point of Superman, is that he's more human than the rest of us in that he represents what an "ideal" human is supposed to be. No one has really "othered" him in his portrayals.
Martian Manhunter on the other hand has to pretend he's someone he's not and hide his true heritage to fit in, that's an immigrant story.
Homelander is a deconstruction. Or maybe a reconstruction depending on how you look at it.
Homelander is what you expect from a superman. From an 'ubermensch'. Superman has been around so long that we forget the creators knew what they were doing when they made him.
Every other Kryptonian not in Superman's direct family influence is pretty much some variation of what Homelander is.
The idea is that Martha and John managed to thread the needle to raise him 'right.'
And while he is often mythologized in a way that makes his goodness seem superhuman, not all portrayals go for that. Nu52 and particularly Superman and Lois play around quite a bit with his humanity and fallibility.
Tbf if you want to say that Superman is a product of his environment, then Homelander is a product of his, chances are he doesn't turn out this fucked up if he had a normal childhood.
So how can Homelander be what you expect from a Superman when its been shown time and again that the way he is, is down to the way he was raised primarily (and I'm not excusing it).