I don't think back links increasing SEO applies to youtube videos. I've even heard this is an old system, and that google now ranks sites more on watch time, similar to youtube.
Black hat SEO simply means ways to boost your SEO usually through gaming the system, like keyword stuffing, hidden link spamming and it's usually for short term gains.
White hat SEO focuses on techniques that target a human audience as opposed to a search engine. This can include creating content for humans and doing research on what is trending. It's meant for long term gains
Now in term's of Youtube's SEO, what really matters are titles, descriptions and tags. But on top of that, Closed Captions, translations on your descriptions for various languages, and titling your playlists correctly also add up. Doing research of keywords using the principles of Supply and Demand, knowing your niche, the current trends, knowing how big and relevant your channel is at competing will also play a big factor to your success.
But remember even if you had perfect SEO, this does not guarantee that your channel will grow. You need some sort of initial fire to boost your videos and get watch time, especially during the first 48 hours. Now where do you get this boost? There's your subscribers, random people finding your older videos and then checking out your latest, and there's external sources like promoting on social media and other websites.
What I'd like to know is that if your new video could appear in the front page of someone not subscribed to you if it has no watch time yet. I'm going to assume no.
