As most carriers use averages for baggage weight & passenger weight but actuals for the AirCargo units, the most likely area for weight error is not the air cargo (Frt, mail) load but rather in the bgge / pax weights. I know there is a fudge factor built into the W&B but have always wondered how close the average wt was to the actual all up load (Pax, Bgge & Cgo).
Actual cargo weights that are usually provided by the shipper.
If they are off, then the mistake goes un-noticed. I just learned of a recent air cargo shipment (on a pax carrier) that was reported under by 1500 lbs and not noticed until customs on the recieving end flagged the shipment for inspection because the wt was off.
That's just one pallet of cargo. Add that to the high probability of pax and baggage weights being off and you have a potential beginning link in the accident chain for quite a few flights every day.
I've experienced quite a few Max Gross takeoffs that barely got off the runway with two engines operating. If an engine had failed after v1, the takeoff would likely not have been successful.
So yes, it is possible that AF447 could have weighed more than the crew thought it did, but so do many flights that are operating every day.
A contributing factor? Maybe.
A direct cause? Probably not.