Some Youtubers talk shop on their channels. I have learnt from them that this is not the case. Even if a Youtuber is very meticulous about placing and restricting the ads (e.g. two mid-rolls), sometimes the software "forgets" and goes full ad blast on the viewer (one pre-roll and six mid-rolls). The cynic's interpretation would be that this happens on purpose.
Once I do have the watch-time (4000 hours per year) to monetize, I will feel sleazy about it but I don't think it would make any difference to viewers, I'll just be taking the pennies I deserve.
Oh, wait, you mean you can't monetize without exerting some actual effort? How is that Youtube's fault?
(disclaimer- I work for the Goog)
There were some other creators that I saw some less egregious but still questionable cadences with, which I thought would go against their general ethos (like ads every five minutes on an hour long video by a person who is generally against a culture of over-capitalization).
Maybe A/B tests?
Recently, some people were trying to tell me that ads are entirely controlled by the video uploader, when I brought up some videos that clearly had way more ads than any content creator would reasonably allow.