Mike;
Box or cube vans that have GVW of 10,000 lbs or less are surely a dis-advantage over the typical Sprinter or one ton, 3/4 ton Ford, Chevy or GMC van. That is they are operated legally by weight carrying capacity.
If you purchased a box or cube van with GVW greater than 10,000 - say 14,000 lbs, then you would have the legal weight carrying adavntage over the other vans. Downside - now you have to log because the vehicle exceeds 10,001 GVW and chances are the truck has no legal sleeper.
It's just really hard to have your cake and eat it too with a small cube or box van.
Hope this helps you.