Agreed. These alternate Earths aren't meant to be exactly the same as the mainline Earth. That's the main reasons they exist, to explore Supermen, Batmen, Wonder Women, and others who might not be as perfect as the ones we read in their monthly comics.
I don't expect Kingdom Come's or Injustice's heroes to be as incorruptible as their Earth-0 counterparts. I just expect them to be similar enough that creators can tell stories about they when they fail without it tarnishing the main ones. In the end, the only thing that matters is whether or not it makes for a compelling story. With Kingdom Come, I'd say Waid & Ross largely succeeded. With Injustice, the games completely failed, while I think Tom Taylor did an admirable job trying to salvage that lackluster foundation and spun a few good comics out of it.