It depends, like so many other things on what you mean by “making it”. It is different for everyone and I know a lot of viewers in my own audience are struggling with this.
If making it is getting to 100K subscribers then I’ve seen many of my friends make it on their own and I will be there shortly myself (73K as of the writing of this with 5K/month net growth rate).
It’s largely of matter of “what” is making it or being successful and “how” are you going about it.
I’m not a full time YouTuber even if my volume of content suggest otherwise. I run a full time business, which my channel content also helps to market. I also don’t make popular content. It is a HOW TO channel, so if you don’t need to solve a very, very specific problem that day, then you are not going to watch my videos. If you don’t need help more than one time with that type of issue… you won’t subscribe.
HOW TO channels and education channels that don’t target a niche group or age range are one of the most challenging types of channels to grow on YouTube… yet since doing consistent weekly content in 2013 I managed to do exactly that. I’ve seen other creators like Steve Dotto and Karen Kavett do the same… For a long time Jared Polin did also before building a team.
You can get there Solo, but it might really be a matter of how long you can stay that way.
Everything Hank Green said is valid… however I don’t want you to think that the ONLY way you can make it is to build a team. But to Hank’s point as I inch closer to 100K I will be doing exactly that because it will be how I grow from there and how I maintain my business and my personal brand.
If you are doing YouTube as part of your business, building a team might be the most practical thing you can do, just like Tim Schmoyer is doing now over at Video Creators, after having been solo for a long time.