Youtube wasn't even close to first -- it started in 2005. They were more like third or fourth. Youtube (and later google) got the formula and right -- they learned from the mistake the first movers made.

Sort of like Facebook, Dropbox, Salesforce, Instagram, Google, etc. None of them were first. Being first is dangerous.

The advantage it had was a cavalier approach to piracy iirc. Didn't they use that to bootstrap before going legit?