Most thumbnail debates happen on a laptop at 100% zoom. Viewers scroll on a phone in a dense grid.
If the face, object, and text compete at full size, they collapse into noise at feed size. Always preview small.
A simple rule
One clear focal point. Short text (or none). Contrast that survives dark mode YouTube chrome.
Use ThumbnailTools feed-size preview and heatmaps so you are not guessing.