Across 5 funding rounds, Crunchbase lists Loopt as having raised $39 million and then was acquired (acqui-hired?) for $43 million. He didn't create any multiples of value for his investors. Loopt wasn't a breakout hit like so many other YC startups have been. It was certainly one of the first interesting location-based apps in the App Store, but soon was surrounded by other location-based apps and never really appeared to surface and gain traction.
Obviously Sam runs YC now and has dramatically improved it, but in the lens of being an entrepreneur, isn't he still essentially unproven, and not a success story in the startup world?
Support players on the other hand, are relied upon to support the carries by getting supportive items, maintaining control over the map (fog of war is in effect), being in the right places at the right times so as to provide their carry with space to work, and generally staying at a higher level of awareness in order to make more of the big picture calls. Most teams' leader will play a support character.
I suspect something similar may be at work here, in that he is very good at choosing and supporting "carries". There are probably very many people in the world who are very perceptive, empathetic, and can achieve a high level of understanding, making them well-suited for leadership positions, but without luck in addition to giving it their best effort, are never put in a position to shine. Just because someone will never be a top-tier carry, doesn't mean they can't ever be a top-tier support, but our society tends to demand the former before you're trusted to do the latter.
Or not, just thinking out loud here. :)