The execution being nontrivial is not in fact the main reason why you can't just “claim their kingdom”, their biggest most is by far the network effect, not the technological challenges (which also nontrivial, is far more tractable today than it used to be when YouTube was founded, and even then it still only required 67 employees to build from scratch).
Unless you think the initial YouTube team that was acquired by Google had 67 engineers and nothing else, I don't get the point you're making here.
The fact that you can in fact execute (whatever you want to put in this) a YouTube alternative with a team of less than 100 is easily demonstrated by the fact that YouTube used to be this small at some point…
The execution isn't actually that difficult for things like Facebook and Twitter. As pointed out, it's a network effect thing; the same reason Bitcoin is dominant despite there being alternatives that are orders of magnitude better on every metric.
The cost per user to run most of those platforms is in the pennies range. Certainly under $4 / year / user.
Compare that to the cost of leaving our vulnerable minds - our parents and grandparents, or angry loners, etc - to the likes of Ben Shapiro or Jordan Peterson, who YouTube is weirdly obsessed with.
YouTube is a bit more expensive to run, sure... But the total cost is still a tiny fraction of the tax take, were we to fund a free and fair alternative ourselves.
Btw, expecting a fully viable alternative from a single person before you ever start exploring criticism or alternatives is wildly silly, imo.
As I already replied to an adjacent comment, the execution includes designing in those network effects and maintaining/modifying them over time. It also includes the moderation, marketing, operations, etc. It's literally everything beyond just the idea.
Furthermore, in no way have I stated nor implied that I expect an alternative must be implemented by a single person. I think your least charitable interpretation of my comment is wildly silly.