Cars are marketed by car manufacturers as a safe and reliable way of getting from A to B; Youtube is (to my best knowledge) not marketed by Google as a source of safe and reliable life advice. The better car analogy would be someone who procures metal plates, household cleaner and a school textbook with an illustration of how internal combustion engines work and winds up blowing themselves up with the creation, and even there the textbook author still puts more of a society-backed stamp of approval on the content that was employed than Google does.

Which would seem to speak directly against the idea that Google aren't allowed to police the medical advice being given on their platform. After all, they're not marketing themselves as a safe source of medical advice, so there should naturally be no standards preventing them from controlling what's being displayed.

What do you mean by "aren't allowed"? I'm not disputing that they are allowed to: otherwise I would bring a lawsuit, rather than arguing against it on the internet (as I am, and I believe I am allowed to). Perhaps, though, they should not be allowed to, being the de facto monopolist on user-uploaded video in the anglophone world they are.