When he wrote this blog series, he was writing for entrepreneurs, and specifically entrepreneurs that a16z might want to fund. When you're an entrepreneur, a.) you can't do anything about the people anyway, because it's you and you can't exactly get rid of yourself and b.) one way that you can improve the founding team if you are it is to make decisions that will put you in a big market that needs what you're making. And entrepreneurs that listen to that and heed it will be good candidates for the service that a16z is offering, which is support in scaling a company to take advantage of a big market.
When you talk to the press, you always want to talk about people first, because you come across as callous and nerdy otherwise. Journalism is all about finding the human angle; if you frame what you do as "we find good people and support them", you get a lot more public support than if you frame it as "we find unexploited market opportunities and exploit them."
And then true success comes from those products that make a new market, since almost by definition they have great product/market fit.
"Personally, I'll take the third position -- I'll assert that market is the most important factor in a startup's success or failure."
seems to be at potential odds with what I've seen Marc say in a lot of recent interviews he has done. Over and over again, he'll very specifically focus on the people being the single most important thing, when he discusses what matters the most.
For example, he reiterates this point about people again the other day ("most of what we do is evaluate people"), in this excellent Bloomberg interview podcast:
https://www.bloomberg.com/news/audio/2017-05-19/interview-wi...