Interesting you mention that, because I've been debating whether to use words in my thumbs or not. Check out the recent vids on my channel "using magic to feed the homeless" and "taking awkwardly close up pictures". I think those are actually super eye-catching thumbnails because of the way I did the text. I posted the recent "superbowl interview prank" without any text at first, and it actually didn't do that well (the audio sucked, but that's besides the point). I've really been debating what to do about the thumbnails though. I'm friends with Stuart Edge (we're about to do a collab), and he never puts text in his thumbs, and is one of the top channels on Youtube right now.
I dunno, you make a good point though. I've been giving the text/no text thing a lot of consideration lately, so thanks for your input.