The problem with this is that the thumbnails usually also contain helpful information.
As an example, a recommendation from ARTEde with the title "Poor despite job | ARTE Re:" where the thumbnail shows "Brits at the limit" and someone standing in an supermarket aisle.
Or the title "TSMC's First Breakthrough: The Copper/Low K Interconnect..." with the thumbnail "COPPER SEMIS" on top of a magnified semiconductor.
This means that it's the community that sees sensational thumbnails and changes them to some other thumbnail. By default dearrow shows random thumbnails if no other were provided by the community. But you can disable this and show original thumbnails, but if there is a community submitted thumbnail it will show the community submitted one. I think for example the arte thumbnails won't get changed to other thumbnails as they are not sensational/clickbaity/mouth open.
There are extensions that can swap the thumbnails with a frame from the video. It's not as good as a handpicked frame, but it's a lot better overall compared to the garbage youtubers are making now. The one I use on chrome is called "clickbait remover for youtube"
