But could a team of smart people with access to 300 million users build a video streaming platform that’s profitable?

How big of a team are we talking about?

A small team, no.

First there's compliance with copyright laws to consider, All the false accusations that go along with it. You gonna need some lawyers and support people to handle these issues.

Moderation is significantly more challenging too. It's significantly harder to detect things like copy right violations, child porn, etc, when it's in video forma than in text form.

Then you need staff to manage the clients. And by clients I mean the advertisers. So there's going to have weird demands like "no swearing in the first 15 seconds of the video" or whatever. And so you have to manage the rollout of weird features like that. Which ideally would include tools so the content creators can remain in compliance with the weird demands of the advertisers.

Then there's the bandwidth considerations. It takes way more resources to serve up video to 300 million users than it is to serve up text.

Sure many times Youtube sucks at these things right but these are things that need to be done and doing them right is going to require a larger staff than YouTube has.