Nebula has about 10.000 videos, from only select creators. Youtube has around 1 billion videos, and everyone can upload. Nebula is not actually a Youtube alternative unless you’re in one of two specific target audiences:
Already established educational content creator looking for alternative platform
Person watching educational video content and not much else
I don’t see Nebula opening up their site to everyone and letting anyone upload content any time soon, and for that reason I don’t see them as a Youtube competitor at all. They’ve found their niche with curated quality over quantity.
Fun fact: The difference between 10.000 and 1 billion is… around 1 billion.