flying out of a performance challenging airport we use real bag weights. so yes when i sign the loadsheet i can tell you how many and what they weigh in each hold. We use standard weights for passengers.
In terms of hand luggage that`s why there is a weight limit! we use an average fiigure so it should even out over the flight. If weight is a problem then on smaller aircraft you can always even ask for every passenger and hand luggage to be weighed! and use real weights. Average weights work better with more pax. Average weights used are approved figures that are correct for the type of flight you are doing and are checked to ensure that they are correct.