You mentioned aft cg as leading to a flat spin... from the report the a/c was close to the forward limit on departure.
Modern transports are designed with supercritical, or aft loaded airfoils to give thicker airfoils, (more fuel volume and reduced structural wing weight), compared to conventional airfoils. Think of these airfoils as conventional but with 5 to 10 degrees of flap deflection. Even with the long moment arms of the tail of transports, there can be up to a 20 count drag penalty to trim the nose down pitching moment produced by the aft loaded, cambered sections, at cruise. To mitigate this drag penalty, designers will trim at aft cg positions at cruise using fuel transfer. The pilots here can expand on procedure, and whether they would have been at max aft cg accounting for fuel burn.
We normally reference aerodynamic conditions at 25% MAC, so cg's approaching 40% are pretty far aft. Don't think even aerobatic airplanes are operated at 40% aft cg, but will check.
Edit: For the Yak 54, cg can approach 37%, but their forward cg limit is 29%. Must keep it aft for maneuverability. Abbreviated paragraphs,
Personnel from the Yakovlev Design Bureau provided the following information: The airplane is rated for nine positive Gs, and seven negative Gs. It has a roll rate of 340 degrees per second. Yakovlev Design Bureau personnel reported that according to their flight test data, at an aft center of gravity (CG) of 37 percent mean aerodynamic chord (MAC), the airplane exhibited neutral stability, but was easily controlled. At a forward CG of 30 percent MAC, the stick force per G is 4 kg (8.8 pounds). At an aft CG (37 percent MAC), the stick force per G is 1 kg (2.2 pounds). The airplane has an aerodynamic buffet that occurs before a stall. The altitude needed to recover from an upright stall was 820 feet, and 984 feet for an inverted stall. The airplane did not demonstrate any tendency to enter an inadvertent spin during stall testing.
Additionally, Yakovlev Design Bureau personnel reported that upright and inverted spins were steep and stable. The angle of attack during a normal spin was 40 to 50 degrees, with a recovery in 1/2 turn. The altitude loss for a 3-turn spin was reported to be 1,969 to 2,133 feet. The altitude loss for a 6-turn spin was 2,625 to 2,789 feet. The load factors during spin recovery did not normally exceed 2.5 Gs. A flat spin had an angle of attack of 60 degrees, with 1 turn for recovery. The altitude loss during a 6-turn flat spin was 2,297 to 2,461 feet.
The AOA for normal stall can be reduced by relaxing back pressure slightly, but still keeping it stalled. Speeds rotation. Notice that even with low mass at the airframe extremities, it still takes one turn to recover from a flat spin. The Yak-52 takes 2-3 turns. An A330 with distributed fuel load and passenger/cargo load would be extremely difficult, if not impossible, to recover from a flat spin even with larger controls.