the A8s too heavy! thing seems to have a life of its own, my guess the Imp/US thing (which accounts for ~250lb error) started it off and chinese whispers have led to the
A8 is 1000lb too heavy! (I'm not kidding, ive seen this a couple of times.) this is what happens if you dont refer to source docs then get your calculator out ...
our A8 is either ~20lb too heavy, or ~35lb too light, depending on whether we have the winter emergency equipment onboard, according to 2 original docs ive seen. I'd wager most AH pilots are carrying at least 20lb more than the average WWII luftwaffe pilot

our A8 chart is based on 9682lb and shows speeds ~10mph slower than test docs using an aircraft with less fuel onboard. it is even slower than tested A8s with even less fuel onboard ... which all makes sense.
other stuff like acceleration, turn rates etc ... not quite simple, but HT has test data for engine power, weight distribution, max speed, climbrate, stall speed etc so you can work back from there to get something realistic.
I can understand people questioning control surface authority, stall behaviour, E-bleed during maneuvering and other subtle stuff because you ultimately have to infer from the aircraft design and first hand accounts (I have doubts about the XVI compared to the IX/VIII but its not a simple matter of producing a WM test document to prove it), but when it comes to the basics like weight you have to start with the assumption that HTC has got it right.