It varies pretty widely, but Levie's number is on the low side historically for tech companies, particularly for such a relatively young company.

Gates had 45% of Microsoft the day after their IPO. Larry Ellison still owns ~20% of Oracle. Google's founders still have ~10%. David Filo even still has around 9% of Yahoo (Yang & Filo had closer to 20% at the time of the IPO if I recall). Bezos still has around 18% of Amazon. When Dell IPO'd, Michael Dell still owned a huge percentage of the company at IPO, over 40% if I recall (he sold most of it high, which is why before they took Dell private, he was nearly worth more than the company).

If you keep bleeding money and needing more cash influx to extend the runway - then the achieved (and appropriate) percentage rapidly goes to zero.