The market cap of Bitcoin is above 120bn USD, less than Apple and Facebook but more than Netflix. But that is still only about 0.1 to 1 % of its potential. So, big but in its infancy.
Besides it being completely different in other ways, the market cap is not value. You couldn't realize a tiny fraction of that without tanking the market cap.
The opposite also applies: You couldn't buy up a large proportion of Bitcoins without the price skyrocketing. Prices are determined at the margin, what the marginal seller (probably miners) will sell for and what the marginal buyer will buy for. They are the best measure of "fair value".