You are making the argument that because centralized systems have been proven to be able to solve certain kinds of problems in an acceptable way, that it follows that centralization was the magic bullet that made the systems successful.
This argument is analogous to saying that because all wars that have been won to date have been fought using swords, that all future victories will be won with swords.
In the myopia of any era, such statements seem trivially true, yet they are shown to be false again and again.
Let's break down what Youtube actually consists of: It's a hosting platform for videos, a security model, a content recommendation/discovery platform, a piracy/abuse prevention moderation system, an advertising platform, and an affiliate platform (content creators make some of the ad revenue).
All of these can be created as federated systems. There are some significant inefficiencies that give a federated system a bit of a disadvantage, but building it in a decentralized way also offers tremendous advantages.
Such a system will certainly replace Youtube at some point in the future as long as each of the mechanisms Youtube offers is available and performs with similar quality to what Youtube offers.
We've seen some fairly remarkable examples of distributed cooperation (blockchain systems) that many would have thought impossible a few years ago. Critics of such systems still point to centralized control as the inevitable way of humanity, but get proven wrong every day as decentralized systems gain credibility.
Credibility is the key. You are right that the average person who wants to flip around and watch funny content doesn't care how the system was built, but average users do care about the massively annoying ads, the freemium model and the myriad dark patterns that try to squeeze every last penny out of the ecosystem.
Analogous to how Microsoft took a big nose dive soon after reaching "peak annoying" with its tiered OS offerings, $1000 office suite and many other gimmicks that signal impending disruption, Youtube is getting very close to this pinnacle.
The little gimmicks that gradually autoplay you toward the most viral content and ads are pernicious dark patterns that create psychological pain for users and even though they are viewed as successful by the "engagement and profitability metrics" approach, they are creating a bigger and bigger void for some other service to fill.
The problem is, Youtube has created a category leading centralized product, which is now very easy to replicate. Just as Bing was able to easily steal much of Google's search market simply by copying many years of Google R&D in a few months, playing trending videos with interruption marketing is now a known product and any missteps can result in massive loss of market share. Google knows this and will not take risks to expand the platform's features.
So all it takes for a federated model to succeed is some insight into the things that the market wants that Google is too blinded by dopamine-fueled ad watching to worry about building.