Youtube premium is not ad-free.

It is.

I don't why people say this. They even include their own version of sponsor block, which is generous, because technically sponsor segments aren't even part of youtube, they are purely the creator deciding to make the ad part of their content.

Also, just to put it out there, many creators would likley be able to cut sponsored content if the 40% of viewers not viewing ads paid up. Not every creator is a greedy ruthless overlord, many just want to keep the lights on. Especially in tech/nerdy channels, where ad block use is the highest.