Bogle could certainly have been a multi-billionaire. He could have founded Vanguard as a for-profit company and charged high fees. However, that wouldn't be like Buffett. Berkshire Hathaway doesn't operate on a percentage of the company's value going to Buffett every year.
In fact, Bogle took a similar path to Buffett: an investor-friendly path that meant little salary or fees going to them, but a great value for investors. It seems like the difference between them would be attributed to difference in starting point and differences in returns. Since 1964 (when Buffett took over Berkshire Hathaway) through 2017, Berkshire had an overall gain of 2,404,748%. By contrast, the S&P 500 only hit 15,508%. If Buffett and Bogle both started out with $1,000,000, Buffett would have ended up with $24B while Bogle ended up with $155M.
I don't think Bogle could have been a multibillionaire like Buffett unless he either 1) charged a lot of fees for Vanguard; or 2) actively managed his money to do significantly better than the S&P 500.
Don't get me wrong: Bogle has done amazing things for society by pioneering low-cost index funds and offering investors the investor-owned Vanguard. I just think it's fair to point out that Buffett's billions don't come off the back of fees or salary. The thing that made Buffett richer was the fact that Berkshire Hathaway has hugely outperformed the S&P 500. If Berkshire had gotten the returns of Bogle's S&P 500 index fund, Buffett would be rich (as Bogle was), but not a multibillionaire.