Production value is like 1%, lol. It's all about the luck. There's dozens upon dozens of videos that go viral just because it landed in the right person's hands. Example Jon Sudano has gotten over 200k subs in what a month? And all he does is sing smashmouth all-star while "covering" other songs. (IE Adele, Kanye, whatever). Production value equates to staring into a webcam and that is it, no cross country travel bs like Casey. (don't get me wrong, not hating on Jon... just sayin it's not the money that matters)
I would put it at 80% luck, 19% content, 1% production value. Your content initially has to be good enough to warrant "enjoyment" while going viral, then you need luck to go viral. Production value comes in for genres that can't have good content without spending for it.