Ok. Here’s what happens with both these systems.
The bearings die. They may seize (and do) and because the crank axles are carried on plastic spacers in both systems it’s perfectly possible to keep turning the cranks without really noticing.
Shimano use a 24mm steel axle which means the bearings in the BB are bigger and tend to last longer before they seize and the steel axle is much more resistant to wear when the bearings do eventually seize.
The crank axle on a DUB crank is aluminium. When the bearings seize and you don’t notice, you wear a groove in the axle. The system has slop because the axle is loose on the bearings, it feels like you’re bearings are worn and the additional load from the sloppy axle fit wears bearings down at record speed.