I'm not sure why you brought up reviewing the videos. I couldn't find it as I glanced through this thread. If YT was 100 different companies competing against each other, then there would be positive effects as each on tried to out-innovate each other. They wouldn't just be 100 static mini YT's..and if some of them did that they wouldn't make it.
The scale of the company prevents meaningful competition, that's the issue, not necessarily that they can't affordably review the 49 years worth of video.
This whole debate originated in some people noticing that there was a lot of wrongthink on the internet and then starting to yell at tech companies for not fixing it. But it turns out that problem is legitimately hard and the tech companies don't have a magic wand, so all their attempts have been ham-fisted disasters that trample all over everything like a frightened elephant.
That problem in particular isn't really one that competition would solve, because it's fundamentally a demand for censorship, and more competition would make censorship harder. Which is maybe a good thing anyway.
The scale of the company prevents meaningful competition, that's the issue, not necessarily that they can't affordably review the 49 years worth of video.