If YouTube were spun out tomorrow, would they make the same choices in how they source ads? If Google’s exchange is actually servicing the highest quality ads, then great. But if they’re only using it because it’s Google’s it becomes more suspect.
Even if they spun off the most likely scenario is that YouTube would just create their own ad infrastructure just like every other major tech company. They're not going to give away some of their margins, especially at that scale.
Right now they have the advantage that their parent company Google deals with the ads infrastructure for them without any hit to their margins since all the revenue rolls up to the same company anyway.
Even that could be a better outcome. When I worked at Microsoft we often had to “dogfood” some other team’s product even if it was vastly inferior to the front runner. Orgs past a certain size give their managers too many brownie points for making “one solution” that serves the whole company poorly.
