YouTube is a behemoth of a company so you’d expect most of the ads money to go to the creators but you can be sure it’s not.
They also demonetize videos for stupid reasons more and more, and they use their quasi monopole on the video hosting to push ads down our throats in many ways with less and less control over the type, placement or duration of the ads they greenlight because what are we gonna do? Go on vimeo or dailymotion?
On the other hand, sponsors pay the creators directly or through affiliated links, they work even if the video is demonetized, creators can decide whether or not they agree with the sponsor content and remain somewhat in control of how the sponsor sequence is gonna be in their video since they’re the ones making them.
Morally, you can decide you hate YouTube and its ads while still wanting to support the creators (or not) but all users are not on the same level of technological knowledge and might not know what sponsorblock is gonna block exactly (despite the name) or how to set it up.
For those users, I think it’s not a bad idea to have such a warning/opt-out step in the setup process.