The chain tension is the highest load on the hub short of really big bumps. That suggests the problem is definitely too much bearing preload. The pitting which is evident on the rh cone is a fatigue failure stemming from an excessive load being applied and reapplied every time the bearings rolled over the races.
When you get a new hub or wheel, try testing the preload by clamping a stack of washers to each end of the hub with the quick release and adjust the skewer for proper closure to compensate for the slightly different thickness of the washers vs your dropout. You should feel solid contact but no drag. Then readjust skewer closure when you reinstall the wheel.