The irony is in how the US claims to be all about equality and opportunity. But then it treats one of the most productive classes of its residents as second class who do not deserve some basic legal protections.

Still, to answer your question, the difference is in the number of dealings an immigrant has to go through and the consequences if any of these goes badly. If you mess up your DMV meeting every 5 years, no big deal. You failed to update your address in your annual license renewal as an immigrant? That is a potential black mark that can get your green card denied and your life ruined.

Maybe it is the case for every country to treat immigrants like that. But when the US is built by immigrants, it should have an incentive to do better than that. Otherwise, why would people immigrate here instead of all the other "desirable" countries, or maybe just come back home? In such situations, sure, the US hasn't done wrong. It simply had done worse than it used to. And that can be a subjective sign of decline depending on how you look at it.