According to the video you linked, AdSense and in-video ads are basically tied for income (26 and 27% respectively). Both of those are significant sources of income!
In the video I linked, "Sponsored projects" is a type of in-video ads, where they build a particular PC and the video is sponsored by a hardware company, so the total for all types of in-video ads is 41% vs 26% from AdSense.
For smaller Youtubers (LTT is a very large channel) the gap between AdSense and in-video tends to be wider. I don't have hard data on this but it's the result of talking to several youtubers in person. If someone has the data, it would be cool to share it here.
