By now, this claim has become a marketing lie. Pretty much none of the 4th gen jets have accurate flight models. They are all made up.
The only common denominator is that a new airframe has to have an even more broken, OP flight model than the last one. Just simple powercreep, so that new planes (or premiums allowing you to grind them) sell better.
You could argue that they are often classified and it’s impossible to make them accurate. It’s true. However, currently they are so obviously inaccurate, that it’s laughable to suggest they are realistic, sometimes breaking the laws of physics in obvious ways.
In a merge, the difference in flight models can be so big, that you have to hope your enemy is a complete beginner (with wrong instincts) or you might as well give up. With the enemy plane often outperforming yours in areas where, in real life, your plane is better.
To this day there hasn’t been any attempt to implement proper fly-by-wire or relaxed stability, which is one of the defining features of 4th gens, much like stealth is for 5th gens.
Every single plane overperforms in the supersonic regime.
Pilots and airframes can withstand pulling 18 Gs without taking any damage.
Aircraft are often added with missing MFD screens and incorrect or straight up non-functional HMDs. Lots of aircraft with NCTR can’t actually display that information in the cockpit and you can’t use it in Air Sim without the game UI.
I think Gaijin should decide whether War Thunder is still a sim-cade or an arcade game with surface-level realism and powercreep slop (always has been?).