The only time a 2x4 will even come close to a 4x4, whether bathtub bottomed or rail framed, is if you drive the bag off the 2x4 resulting in drastically reduced life expectancy of the machine. if you hit a tough spot hard enough with a 2x4 to get though you can hit the same tough spot with a 4x4 and virtualy ease your way through it not harming the machine at all.
That might not make any difference in a battle-field situation where completion of the mission is tantamount to equipment salvation but in my world you will never convince me that a 2x4 can equal any 4x4 in off-road use...in 50 yrs of construction, oil field exploration, farming, and rough country hunting I've pulled a few miles of winch line to stuck 4x4's...not so much to 2x4's, we just hook a cat to them because that's the only way to get anywhere.
4 x4's rule the roost in the bush. But in truth for the most part they are more expensive, with poor mileage and added complication to boot.
I've blown by a few 4 x 4's laying belly down in the mud...in a 2 x 4.
I ran a 7.3 IDI diesel 2 x 4 with a set of tire chains in the toolbox + winch in the front all over western Canada working rigs. North country too, you have to be more cautious than the 4 x 4 guys obviously. But the 3-5 % of the time that a 4 x 4 is advantageous is somewhat negated by the expense and complication of design.
A fleet of those Klubwagons would have been fairly easy to keep fueled, serviced and in the field in WW2