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.
Ads are a revenue stream mostly for the platform e.g. YouTube itself. You can have a look at this[1] or any other "how my YouTube channel makes money" video to see that's the case.
In-video ads, on the other hand, are indeed a significant revenue stream for creators, but those have nothing to do with the platform and everything to do with the single creator.
[1] https://www.youtube.com/watch?v=-zt57TWkTF4