I think it's pretty clear that "trending" videos are manipulated. I've seen a video with 10k views and five times more dislikes than likes show up in trending.
Unless you know the algorithm for how "trending video" is selected -- I certainly don't -- you can't say that that's "manipulation." Is it a number of clicks over a certain period of time? What's the period of time? How many clicks? And most importantly, how much of what any given user sees as "trending" is based on contextual information: what they've most recently watched, what they tend to watch on average, what channels they're subscribed to?
An awful lot of discussion around YouTube and human curation/moderation elides just how much content they're dealing with; the most recent figures I've seen -- which are over a year old at this point -- show that about 500 hours worth of video is uploaded to YouTube every minute. If we figure an average video is about 15 minutes (a 2017 statistic I found suggested that "the average length of a first page YouTube video is 14 minutes, 50 seconds"), that's 2000 videos a minute -- over 30 a second.
Is it impossible that YouTube employees have secret levers to raise and lower the profile of individual videos and channels? Of course not. But it's absurd to think that such manipulation is common, let alone corporate policy.
To me the problem isn't that flat earth videos exist on Youtube, but the implied "legitimacy" of the recommendations, along with the typically addictive UI elements like autoplay. Flat earth / Nibiru / etc insanity has always been on the internet, but when you saw it, you knew that you were in some obscure corner of the internet that was not normal. If anything, YouTube's insistence on mixing brand-safe, front-page recommendations along with content-adjacent recs lends credibility to the (many fewer now) "rabbit hole" recs. If you're on "Tony Blair is a reptile.mp4" and all you see are things like "Tony Blair is ACTUALLY a hologram.mp4" with 2k views, it's like "whoa, this is weird". But if you get 3 reptilian recs and 5 TED talk recs that have millions of views, maybe it seems more normal? I'm not sure.
Not only is it manipulated, it's flagrantly obvious. PewDiePie for example trends in many countries except the US [e.g. 45 times in Canada, 42 times in Germany vs 1 time in the US], and it's not just him either but many "controversial" channels.
Apparently dislikes count almost as much as likes for popularity - videos that evoke an emotional response are considered better by YouTube. It's a general trend in social networks, because it leads to more views, and one of the causes of the current environment of polarization and toxicity.
