>Sometimes I wonder about how unfortunate perhaps it may be that a language like English became the “default one” for the world. The language is so sloppy with accents and different pronunciations that people can use tiny differences to “other” people based on social status, geography, and so on.

It arguably became the default international language of trade because it's so sloppy, and more precisely because the language is a mish-mash of other languages, readily borrowing words from everywhere, and this is why it seems so sloppy. Some other, highly regular language like German would never have become the international language of trade because those languages aren't sloppy, and so aren't very good for non-native speakers to use daily, and aren't products of a culture that got rich from trade.

As for tiny differences in pronunciations being used to discriminate against people, try learning German and moving to Germany and see how the natives treat you. You'll always be an outsider there, because you're never going to learn the language or pronunciation to that level as an adult, and the culture is known to be pretty insular. English-speaking cultures are generally far more welcoming to immigrants and people who don't speak the language like a native, and it's pretty easy to understand "broken English", which again is part of why it works so well for trade.