I am not surprised the discussion has fizzed. Pilots don't get to see what goes on behind the scenes. Neither for that matter do most flight/cabin crew.
Some time spent chatting or preferably watching a load master and a load controller in action followed by some time watching the loaders in action might change that.
In the meantime start building your own data base of over weight operations. That is not necessarily over maximum weight per se but over load sheet weight. You can do this quite easily on FMC equipped aircraft.
Check the flight progress preferably on time. If early or late make a correction. If on time and at altitude on track but down on fuel. (CFP total) and below fuel burn (CFP).
You can check the drag by simply checking the flight control indicators are in the flight position and not causing unexpected drag.
Check the actual fuel flow in flight required to maintain CFP (Company SOP cruise). (Econ/LRC etc).
Check the thrust required for a given CFP (FMC) weight in flight and compare to actual power being applied to maintain Cruise. This will confirm you are heavy. But how much heavier?
Alter the weight in the FMC down a few hundred/thousand poinds at a time until the CFP fuel flow is achieved. Then note the difference.
That iis an indication of how much heavier you are right now. You will have to exptrapolate back to take off to get a take off weight.
Trim? Bad luck old chap, the load sheet is always correct!