That's definitely not the case. It's one of the areas where FSX/P3D are way off. Just at baggage/fuel etc. at their 'correct' locations and you will notice that their effect is greatly exaggerated.
It's most likely related to the faulty FSX/P3D inertia calculation/simulation.
The apparent exaggeration comes from misinterpreting the Cm vs AoA table. It is for the whole airplane, not just the wing. 99% of all flight models for this platform suffer from this. You can absolutely use real weight and balance. My procedure goes like this,
Everything in the weight/balance and geometry sections is set accurately using real world numbers. The Cm0 is set to give the correct trim speed in the empty configuration ( minimal fuel and no payload, set fuel flow scalar to 0 ). Then, the airplane is loaded with a payload and fuel, the CG determined. The wing/tail combination is analyzed using CFD software to determine the new trim speed. The slope of Cm vs AoA is adjusted ( usually doubled or trippled ) to give the correct result. In turn, you may have to go back and redo the Cm0 value and repeat. But, after a few iterations, you can nail it down. Elevator and trim effectiveness usually have to be increased as well. Voila, there is no exaggeration. The Cm value near Clmax should be somewhere around 0.4 or higher. That corresponds to a tail efficiency of about 40-60%.
You also need to know things like the lift slope of the 3d wing ( from airfoil properties, zero-lift angle, aspect ratio, sweep angle, incidence, twist, etc ) and the lift slope of the horizontal tail, affected by downwash from the wing and tail aspect ratio, incidence, etc.... As I said, I use separate software to determine those things, which I suppose not everyone has access to or can afford. Such is the system we have to work with on this platform. I guess you could do something similar in a spreadsheet, using appropriate lift slope formulae, calculating moments based on CG position.
Basically, the lift slope of a 2d wing is 2*pi per radian, or 0.1 per degree. For a straight 3d wing, you could modify for aspect ratio as 2 * pi / ( 1 + 2/Aspect Ratio )
You could modify further for sweep by cos(sweep angle).
Then, downwash angle ( rad ) is 2 * Cl / ( pi * Aspect Ratio ).
This will get you in the ballpark, if you don't have CFD software that can analyze a wing/tail combination in 3d flow. I'm using Multisurface Aerodynamics by Hanley Innovations.