Very few companies have gotten to a $30 billion market cap in 10 years.
The main reason is everyone else sold or overreacted to the market and pivoted.
Yammer sold for $1B+ to Microsoft but could've easily been a 30B+ market cap company.
Slide had some issues and continue to react to the market trying different things - had they focused on a real problem, they might've created a Zynga type company.
The rest of them (Dave @ 500 Startups, Jeremy at Yelp, etc) are still at it and the verdict isn't in.
That being said, the fact that 1 company has an alumni with such success - and There's many I haven't mentioned - is only testament to the quality of the people.
P.S. What's the market cap for Tesla? Elon is just getting started - I think I'll be WAY bigger than LinkedIn.
Network Effect. The more people who join a network, the more valuable it is for the next person to join, and so on.
Compare LI and FB stock price to GOOG for example, and you will see these social networks are 6 times more valuable (relative to revenues) than the more transactional sites that don't truly connect people in a network fashion.
I wouldn't consider LinkedIn as the biggest success from the PayPal founders. Peter Thiel did pretty good, especially because he was one of the early backers of Facebook.
But when it comes to the individuals, Elon Musk's personal net worth is double than Hoffman's. I would say it depends on how are you measuring success exactly.