proof? RACQ should do.
Caravanning Queensland: Towing
The racq link covers the mistake in your second link where they forget to subtract the ball weight from the carrying capacity of the D4.
I know you refuse to see any wrong but you cannot add and/or subtract the same number twice.
In your first example you have both the trailer and ranger at 6ton 
GCM.TICK
You then state "
GVM (with max towing): 2,500kg - Vehicle Tare Weight: 2,159kg = 341kg" again correct.
Heres where you got it wrong;
To be able to tow, 3.5T with the PX Ranger you need to take 
700kg(Buzz wrong its 700kg subtract towball weight transfer:eek: )out of your maximum allowed 
GVM figure of 3,200kg. If you then look even further into the vehicle specifications it is even more of an eye-opener. Lets assume that you are still towing the maximum amount of 3.5T with the PX Ranger which we will say is a Dual Cab XLT.
 So you are now left with a payload of 341kg. Lets take out a couple more essential items from that figure.
 Payload: 341kg - 
Tow Ball Down Force Approx: 280kg - Buzz-XXX, You have already added the total trailer mass into the GCM , you cannot again add it to the utes weight, that is a separate issue.  
Why are you refusing to accept if you take 250-350kg out of the trailer and put it into the ute, via the towbar, your still having the same GCM? 
Your second examples table 
CONTRADICTS your first giving,( actually proving myself and sjane ;) correct) the ranger 300kg load capacity with a fully loaded trailer, direct from 
your link. So which link is correct, factual?????
So using your own links, one at least is wrong , one says positive 300 kg the other is negative 9kg. take a pick :D 
It is not my "opinion" it's 
YOUR stated fact, just pick a fact to back please its either 300kg+(positive) or -9(negative) it is a fair difference.
It then goes on to not take the towball load out from the D4 GVM? Whoops.
You've consulted an independent engineer, I've put up ARB engineering figures. along with RACQ, and google, pedders or tjm for the same info. Who does more in that field??? 
The only vehicle with a decent GVM after hooking up a 3.5 ton load is a defender110(or a f250 monster) which exceeds 650kg load after subtracting 350 kg for towball weight.