It's not the bearing. It's the chain wrapping onto and off a sprocket. With a small idler, the angle each link has to rotate is very large. And it's happening in the taught part of the chain unlike the rear derailleur. But I've explained everything in my original long post. Now this debate, besides being offtopic, has serious vibes of trying to explain things to @seanfisseli, so much so I was convinced @Trocko might be an alterego. Looks like I was wrong about that one 🙂