I generally go on the same theory as davewalsh, if the bearing is full of (waterproof) grease there isn’t room for anything to get in. The little extra drag is worth it as it’s not spinning at 30,000rpm.
Didn’t strip and re-pack the bearings on a new RF BB . The bearings lasted about 150 miles. Never pressure washed, just hose on sprinkler and a soft brush to clean.
The BB was feeling a bit rough so stripped it to find DS bearing a bit rough with some grease in, and the NDS bearing seized and no sign of any grease. The only movement on the NSD was rotation in the top hat. So I wouldn’t assume that bearings come with enough grease for wet/muddy MTB applications.