Actually if you put Vallejo over a primer coat.....the color coat should never come off. Most problems with Vallejo chipping of being soft is because it was either brushed, or airbrushed over bare plastic.
As far as the Air line or Model line of Vallejo flat white, yes the Air line is good to go out of the bottle, but there is no reason the Model Color Flat white can't be airbrushed. Just have to thin it out....no different than any other model paint.
I sell exclusively Vallejo in my shop, and have personally used it going on 5 years now....and for my money, there isn't much out there that can touch it. Lifecolor a close second....but it is harder to get in North America, at least the individual bottles.