There are a couple of questions (otherwise great article). One small is right only as long as it is economically viable. Do you believe Google would still be viable as a search engine if they had remained at 50-100 people size (or whatever you think is the optimum size?)
Second, most YC companies don't yet have business models. That is not a knock on them - I am simply making a statement of fact. Given that many (or most!) are hoping for a nice "exit" from a large company, doesn't their success pre-suppose the existence of large companies to take the other side of their exit trade? In effect, does the YC model (mostly) require the continued existence of large inefficient players? What happens when the (software & internet) world were to be full of small, ultra-efficient start-ups? No exits? (the second question is totally hypothetical - large firms do exist, but just asking to clarify the argument myself).