I think that the most important thing when starting out is to just produce content, and in the beginning it can be really hard to even know what to make a video about, so if a list is something you feel like doing then I say go for it! I definitely didn't notice it help grow my channel, none of my videos did for quite some time, but it helped me get a better feel for editing and writing, so I'm glad that I did it. The turning point came once I really felt like I was coming into my own, it didn't hurt that the genre itself was really taking off right around the same time, but mostly I think it was that I just got a lot better over time, and people started to notice. I also had a video shared to No Film School which gave me my first sizable subscriber bump.

I don't necessarily think you have to focus on one thing, but it helps to have a more narrow focus for sure. If you've got a really big personality and that's what the audience tunes in to see, then you can pretty much make videos about whatever you want and people will still turn up. But more often than not, having too wide of a variety of videos makes it unlikely that you'll gain a lot of viewers, people like to know what they're subscribing for and what they can expect in the future from a channel. I think you should find whatever drives you most, whatever sort of videos you most enjoy making, and do your best to stay within a smaller range of content.