The great thing about sponsorships is that you don’t have to give YouTube a cut. Plus, you can negotiate whatever contracts you want based on impressions and the size of your audience. In most cases, the amount of revenue you generate from sponsorships is substantially more than YouTube ad revenue. (Meanwhile, you can still generate ad revenue. So it’s like having two sources of income from the same video.)
In any case, if you have incontrovertible evidence that YouTube is actually unprofitable today, and why that is (i.e. is it because they’re just investing all that profit back into growth, or are their upkeep costs truly just on the order of multiple billions of dollars?), would love to see it and adjust this accordingly. Doesn’t really change any of the points made though.
And though they don't appear to be huge revenue contributors at this point, the YouTube Red and YouTube TV subscription services can't be overlooked when trying to value the company. Particularly YouTube Red, which provides ad-free YouTube, some original shows and access to the Google Play Music service for $10 per month, and which led YouTube to become the top-grossing U.S. iPhone app in March. Later this year, Google plans to replace Google Play Music -- in many ways Red's weak link -- with YouTube Remix, a music service that's fully integrated with YouTube.