If you avoid watching clickbait thumbnailed videos then you will miss out on a lot of good content. Perhaps you are fine with this but if the implication is that a clickbait thumbnail implies the video is not good, this is an indicator that, at this point has almost no correlation with the video quality. This is because content creators, pretty much have to use clickbait thumbnails to get views or traction, largely because of the way YouTube's "algorithm" works.