I don't agree with this at all. I don't think it's a problem in JKR's writing, if anything, it'd be the character. In this, you mention Harry and Sirius. That's only two characters... so I think, if they really were like this, it'd be intentional. If it were JKR's writing, then every character would be like this, which we see, is not the case.
I feel like you are singling Harry and Sirius out. And I don't know what you mean by inferior. I think with Sirius, you are thinking of Kreacher. Yes, Sirius was not kind to Kreacher, but even Dumbledore says that it's because Kreacher represented the place that Sirius hated, the family that never accepted him. As for inferior, it makes me think intelligence, and I do not think for a moment Sirius thought Snape less able than him. We've seen Sirius hate people who generally deserved to be hated. But he never hated anyone unjustifiably -- Lord Voldemort, Peter, Kreacher, Death Eaters, Snape. With Snape, we don't know the other side of the story. We see them picking on Snape, but I doubt Snape was completely innocent.
With Harry, I think you're very wrong. Harry considers those he hates people. Why do you think he saved Peter's life? Saved Draco's life? He and Draco were never friends, but I don't think Harry once considered Draco inferior or less human than him. Peter was the reason Harry didn't have parents! But he saved his life! Harry even felt sympathy for Voldemort! He thinks of people more than many others in the series, even people he hates.