If NeXt was really successful, it wouldn't have been bought out by Apple, it would have flourished on its own. NeXt was somewhat profitable (after it turned into a software company), but never truly "successful". Jobs did some good innovative things with NeXt, which is why Apple eventually bought it. Jobs also learned a lot more about managing a company at NeXt, just as he did at Pixar.
These days, getting your startup bought out by a tech giant is a measure of success. It means they value what you're producing and the people who are producing it. Why do you think Apple, Microsoft and Google compulsively purchase hundreds of startups with rad ideas? They're not afraid of being toppled, they see a good idea they think could be successful and want it (or don't want a competitor to have it).