What? I can think of several off the top of my head.
J. K. Rowling became a billionaire by writing the Harry Potter books. Oprah Winfrey became a billionaire through her brand as a talented talk show host. Michael Jordan became a billionaire thanks to his basketball skills. None of those are even remotely exploitative.
In the examples you have cited, all of those people were paid for their labor. In the cases of Winfrey and especially Jordan, many of those people were paid extremely well for their labor.
If you consider voluntary association and compensation for labor exploitative, then I'm not sure what to say to you.
By your standard, anyone who participates in the economy is making money off the backs of others. My mother is now happily retired on the savings she accumulated working as a nurse. She couldn't have done that without all the people working at drug manufacturers, EMR companies, or health insurance providers. Did she make money off the backs of the hospital lab techs? Did she exploit the ER security guards? After all without those people, she wouldn't have made it.
Admittedly, you're probably right. I don't know the personal conquests of Dorsey or Buffet, so part of me was hoping at least a little bit that they weren't as ruthless as the others.
J. K. Rowling became a billionaire by writing the Harry Potter books. Oprah Winfrey became a billionaire through her brand as a talented talk show host. Michael Jordan became a billionaire thanks to his basketball skills. None of those are even remotely exploitative.