Sorry, but I don't understand this comment. If exit size is not one of the primary metrics VCs look at and how they define success, I'm at a loss for what would be.
More specifically, how do you think USV and Fred define success? Fred says that financial returns (hence exits) are important on his own btw [1]
Exit size doesn't matter on its own - you have to take into account how much equity you own. 40% of $100 million exit is better than 10% of $300 million - as an example. I would describe the first scenario as more successful than the second.
I am taking this from the founder's point of view, where no money is paid to buy the equity. You highlight the good point that it depends on the context and point of view - who's success is being talked about.
To further my other comment - I'm a regular commenter at AVC.com and Fred generally talks from the perspective of what's best for the founder, for the entrepreneur. This is why I am making these insights.