sounds, for the most part, like user error to me. or, in the worst case, poor assembly at the factory. the problems that you mention (with the possible exception of the stripped axle) are common issues with any hub. not having the cones properly dialed in, of course, will cause play. cones can and will come loose over time, especially if the wheels are ridden hard. and, yes, believe it or not, sealed bearing hubs can have problems too. you really have to make sure that the "cone" (not really a cone on sealed bearing hubs) and locknut are very tight against each other. tightening down a wheel, especially if you torque the track nuts too hard, causes problems with all sorts of hubs. the fact of the matter is that most hubs use a threaded axle.. and, believe it or not, the locknuts and cones can and will move.
you haven't really said anything about the quality of the hubs themselves. it seems that when properly setup, they are more than fine. i'm sure that i and many many others can vouch for the quality of the promax hubs.