The use of debt vs capital is interesting, but one isn't clearly better than the other. You can look at OpenAI's revenue as allowing them to raise investment capital.

To invest in OpenAI is to bet that they won't need to keep investing more in hardware than they bring in. To me that doesn't seem a sure thing, but it isn't obviously wrong either. They are growing revenue very quickly and already have significant cashflow, and it isn't clear to me that they'll need to sustain the CapEx forever.