Actually it is the freehub length that immaterial if we are talking about DS offset. The cassette width is what matters... or more precisely chain clearance in the small cog and derailleur clearance in the large one.
Actually, both are set in the factory manuals by the component makers as is, more importantly, the chainline. There is no wiggle room there for the hub makers.
The spokes can also put leverage on the hub flange (particularly if it is large) and distort the bearing bore. Did the bearings get loose, or did they bind? Why do you think it was material related rather than design related? Several high end hubs use 6061-T6. It's the best hub alloy IMO because of its corrosion resistance and lower sensitivity to notching.
After we halted assembly and contacted the hub vendor we discovered that they had made a running change as they felt, and as you point out, that 6000 series alloys were easier to work with (and cheaper. Bastids). The customer had specified 7075 and when the hubs were produced to this spec the problem didn't occur. It also went away once the hub vendor switched back so, in this instance, I feel pretty confident in saying it was a materials issue.
Having said that, I have also seen this problem because of bearing bore tolerances and because of flange placement and due to the fact that the hub shell vendor was unaware of a slight mod that can be made to address this. We do this with hubs we make in the OE to address this exact concern (sorry, I'm not going to say what it is) and this extra machining step seems to work.
Since we have gone off on this tangent why do you think some hub vendors say that you can not radially lace their hubs? What potential problems are they trying to avoid?