To be "big" on YT, it certainly helps to have a theme. I am tiny on there partly because I made an early decision to not be pigeonholed into a theme. Yet I still enjoy it. I look at my channel as a visual diary. I like knowing I have videos that my son and I made together when he was 10. I have made friends all over the world on there, all the while making $1000 bucks or more a year for the fun. Its all about perspective I guess.