All this nonsense about swapping bearings on the trail is a non-issue. Traditional taper bearings simply dont fail as quick as a unit bearing. If they fail at all on the trail, they have been ignored for a very long time.
As mentioned, the bearing retainers on a unit bearing are plastic. When it fails, it has the potential to do it with style. Simply not the case with traditional bearings.
Specifically to off road, moisture, etc…. Anyone that knows anything about a “sealed” bearing knows the seals are far from SEALED. Every unit bearing that fails will have contaminated and or lack of grease due to this. And once its contaminated, you are SOL. Again, not the case with traditional bearings.
Rust? Yeah, its hell for the bearing to knuckle connection. Unless you are a so-cal flatlander, the bearing will be frozen to the knuckle in short order. As in, just a few years. Unit bearings do often require the removal of the bearing and knuckle to toss on a (very large) press. That means you are trying to destroy balljoints and steering components to get if off. Once again, not the case with traditional bearings. A quick shot of grease and retorque doesnt even require removing the wheel. Even if you are going all the way down to races, still dont have to remove the spindle. And in a pinch all you need is a hammer and a few punches to do so.
Around here (far from so-cal) its pretty routine for unit bearings to go in less than 75k. Lots of gravel roads, snow, ice, deicer…. Rough roads and contamination. All plays into it. And they simple do not last.