It’s usually a mix of both. A strong title and thumbnail help get the click, while watch time, CTR, engagement and audience retention play a big role in how far YouTube pushes the video.
Make sure the thumbnails, titles and hashtags are on point, and stay consistent, then you are good to go.
It is a mix of all, you also need strong hooks because otherwise your audience will bounce.
Sometimes videos that appears to look worse win just because people actually watch them to the very end. I would consider the retention and traffic source first before deciding to change the thumbnail of the vdo .
