That could well be true, I have not access to the dealer's contract with his manufacturer to check how robustly they specify.
However, we included a contractual clause with our dealer that the available payload to us on delivery should not be less than an agreed value. [300kgs]
On delivery as agreed it was weighed on load cells and found to be I think I recall 62 kgs over the maximum weight it could be, for the plated MTPLM.
That instigated a lot of behind the scenes activity, with the outcome of them offering the MTPLM being replated up to the chassis limit, and a request we please settle for a shortfall of the order of 20 kgs; which we did.
Buying in a professional manner, with such vital things contracted, is IMO the only way that will move towards getting the payloads we require. As it is presently offered, it is a meaningless dreamworld figure, IMO one typically pathetic for starters and even that one rarely achieved.