When you have people watch the video at that fast speed and instantly make a decision, you might as well keep the algorithm - the failure rate won't be too different.
Additionally, these people need holidays, managers, infrastructure and an actual flag will probably not instantly be clear - you'll need to point out the specific offence and make a case. You might even need to look things up. Then you'll have to handle appeals and discussions, because changing the AI blackbox to an appeal-less human black box wouldn't improve the situation much[0]. Next, you need people who can understand the specific language of that video - most will be english, but what happens when a Nigerian video is flagged? So you need people from that country or at least familiar with it. Plus infrastructure.
Overall, you're probably looking at something approaching 400 or 500 people, with this very low flag rate. Assuming conservative 30k$/year [1], this is 15 million USD alone. Doable, yes, but its not the no-brainer you make it out to be.
[0] See this case with FB, which was a human error: https://www.nbcnews.com/tech/social-media/facebook-under-fir... [1] Which is probably optimistic for reviewers, but we'll have managerial infrastructure to pull that average up.