Hmmmm.
Let's start with the moisture issue. Vapour cannot condense on the cold metal if the humid vapour cannot get in (or out for that matter). If the seal is good, you will not find condensation inside the bearing. Proof of that can be found by opening the bearings of the two types of square taper BB. You will find emulsified grease in cup and cone BBs when they have been ridden in the wet - whether they have recently been serviced or not. You won't find emulsified BBs in a cartridge BB that's been ridden in the wet unless the BB is way beyond its replacement point.
Secondly, the seals in cartridge BBs are contact seals - rubber wipers. They are splash proof. There are no seals in most cup-and-cone BBs. They are thus not splash proof and water simply drips in. I have had one such BB in my time, a Suntour SuperbePRO which did have a rubber seal. However, on examination the seal was little more than a square-shoulder grommet exactly like you will find in an electrical device where the cord enters the device. Such a seal cannot operate (seal) whilst turning. It would always leak and move water in via capillary action.
Bearings pumping water. Large bearings with big internal voids can pump water under certain conditions. Bicycle wheels with cartridge bearings are one such example. These hubs are constructed of two bearings, one at either side of the hub and a void between the two bearings through which the axle goes. If the bicycle is moved from a warm environment, say indoors, and taken outdoors where it is significantly colder, the air inside the hub shrinks and sucks air into the hub. This air usually travels through the bearing, bringing water in with it. Not through humid air but simply water sitting on the axle against the seal. Needless to say the water remains behind in the grease. The solution to this problem is to drill a small hole in the axle so that water is sucked in through the QR channel along the axle into the hub rather than through the bearing. This makes a huge difference to the bearing life and good hubs will have such a hole in the axle even though the conditions under which this happens are rare and unusual.
The same doesn't happen for a cartridge bearing not assembled in a hub. The void inside the bearing is too small to create enough suction. Most bearings are filled to about 80% with grease although some can be as low as 60% for specialist applications.
Cartridge bearing BBs of good quality have been designed to vent the inside by bypassing the bearing route.
Have a look at my Campagnolo Record BB here.
The shell is loosely fitted, creating a better path for venting than through the bearing seal.
Let's talk about seals.
Before one can understand seals, you have to understand the first commandment of seals:
A single seal cannot separate two liquids.
The two liquids in question here would be water and grease. A rubber wiper seal such as that found on cartridge bearings cannot prevent water from going into the bearing. That's why these bearings perform so poorly in bicycle wheels in spite of being "sealed."
In order to separate two liquids you have to have two seals with a neutral void in between the two.
This is because of the second commandment of seals:
A seal that doesn't leak will leak.
A wiper seal is designed to weep. If it doesn't, it will quickly burn away, loose contact and leak through the gap just burned away. I usually demonstrate this to people by taking an eraser and running it hard over glass. The rubber burns and leaves a trail of molten rubber behind. This is what happens with a dry wiper seal running on dry steel. The "burn" is prevented by allowing the grease inside to weep underneath the rubber and thus lubricate the seal. However, this means that water can weep in too. This in turn is prevented by a second seal as in the first commandment above. The second seal is usually a non-contact labyrinth seal. Shimano hub dust caps are labyrinth seals, not dust caps. Labyrinths are splash proof but not dunk proof. However, this is enough to protect the primary seals from running in water.
If you find the concept of a non-contact seal difficult, form two letters C with your hands The left one will face right and the right one will face left. Now offset the two Cs and bring them closer so that they interleave. Now pretend each one is a ring and they're rotating around each other. If you splash water on them, the water runs inside the groove and drips off at the bottom but doesn't penetrate.
All good hubs will protect the inner seal with such a device. Good BBs too. Some, like the one in the photo above simply uses two wiper seals with a significant void between the two to prevent the inner one from ever running in water. That's why it is important to have a drain hole in your BB shell.
You also addressed bearing quality. I agree that you can get very, very good cup-and-cone BBs that will last a very long time with good maintenance. On the other hand, you also get very, very good cartridge BBs that last a very long time and cost a fraction of what an equivalent cup-and-cone BB costs. And you get very, very good cartridge BBs that cost a fortune too. The Campag Record in the photo is a case in point. That BB has lasted me 200 000 kms so far and is still going. I've replaced the bearings twice, IIRC, but removed the BB umpteen times to regrease the threads because the aluminium cups creak like hell. My other bike has a Shimano UN 54/52 in and that one is silent and apparently immortal.
You mention bearing ball skid. I'm afraid all rotating bearings have ball skid. You cannot have a ball run between two different radii and not have ball skid. That's adequately taken care of with lubrication. Linear bearings (the type in good quality drawers) and train wheels on tracks are the only bearings where there's no relative movement between ball and track and hence don't require lubrication. You can't use that argument here. Your ACBs and my deep groove bearings have exactly the same amount of skid, which is 50% of distance travelled.
I do think BBs have moved on. Some for the better and others for the worse. Cup-and-cone BBs were good but there is an easier way nowadays.
