Niche definitely helps, but it only gets you so far. For example, there is a channel I'm subscribed to called MakerJ101. It's pretty much a super smart kid doing a "technical vlog" which equates to him making and hacking all kinds of stuff. It's definitely niche, but he isn't unique. There is another channel similar to his called Applied Science.
MakerJ101: 5K subs. His camera work isn't the greatest. Seems like he's using his phone for a camera and sometimes you can get dizzy from him bouncing around with his camera as he pans from one part of his shop to the other. The information and the projects he works on is solid and it definitely fills the niche very well. The video quality isn't quite there and I think it's holding his channel a bit. He probably needs to work on his editing a bit too. He's a college student so I don't think he has a whole lot of time to do much about it.
Applied Science: 120K subs. Same kind of videos as MakerJ101, but the quality of videos is significantly better. It definitely shows when you look at his subscriber count. Granted, this channel does some more impressive type projects.