The friction introduced by hub bearings is insignificant compared with other frictions. Up to a certain speed, the biggest impediment is probably the tires. Then above that speed, it's air resistance.

You can adjust a hub's bearings so that they are far too tight, and you'll feel the resistance. And yet if you put it on the bike and ride, you probably won't feel the problem. I'm not saying it's OK to do this. I'm saying that hub friction is not a big concern compared with others.