Most of them started before the platform was oversaturated and before the ridiculous demonetization criteria, though (which affects video indexation, in fact). Doing what others did back then, even if they still do it today, is not guaranteed to result today for newcomers.
As much as it sucks to admit, the 2 easiest ways to become popular on YouTube today is either sheer luck or sheer stupidity, and since nobody chooses the latter on purpose, that leaves one option we cannot really do much with.
One thing I suspect might work, however, is to capitalize on potential trends nobody else has. For example, the game Baba is You is fairly popular, but strangely enough, no YouTuber or Twitch streamer has really gotten deep into it. Vinesauce got the deepest, but still not all that much. I suspect that anyone genuinely interested in the game making a FULL playthrough of that game, something that apparently does not exist last time I checked, will strike gold with this. I saw something similar with a relatively new channel I found, Clockwork, who uploads high-level Sonic gameplay and montages for Smash Ultimate, which is also pretty rare to find, and probably why the channel has been growing much faster than the average channel with less than a year of dedicated activity.
So yes, offering people something they want and does not quite exist and that you are genuinely interested in yourself is a good way to subvert luck and low numbers, albeit not guaranteed.