Honestly a lot of what you're describing is realistic and more a limitation of the controls. Flying with a joystick, most of this is a non-issue as you have more direct control and choice over what the plane is doing. Yaw instability is intended, but noted. I may specifically address this later on.
None of the planes in this demo should be capable of pulling high AOA, especially the MiG-21 and VJ-101. They stall their wings very dramatically with minimal AOA and at low speeds you have the pitch authority to do it quite easily. The best way to fly the interceptors (MiG-21 especially) is to keep them fast. Dropping speed <400 knots is asking for trouble, and <300 you are basically a sitting duck. That is not the regime those planes are optimized for. At high speeds though, they are stable, much more responsive, and generally turn better. The handling characteristics you're describing are typical of 2nd and 3rd generation fighters, as they tended to be built around high speed intercept rather than dogfighting.
The mouse controls will try their best to keep this under control and limit input. They generally do a good job (you should have seen what it was like before), but it's a very hard thing to automate. There is a whole field of engineering around solving problems like this. It's unfortunate the F-20 never got its flight model updated because I think the F-20 would be more in line with what people think fighter jets should behave like. It's a much more modern jet with a very powerful engine (the Jaguar in particular is very under-powered by comparison), and wings designed for high angles of attack. It would have been a very forgiving airframe, and very snappy.
I've been paying close attention to the feedback both demos have gotten. Posts like yours that are well reasoned and critical are important. I like to make sure to recognize them and let their writers know that it's appreciated, as they are the most helpful to the game's development.
Going forwards, I think many people will find the Harrier a comfortable compromise between the two flight models. While it uses a slightly more complex version of the flight model from this demo, its design necessitates a very high thrust to weight ratio and a high lift wing. While it's not the most nimble thing in the world, it is a very easy and forgiving plane to fly, with ample thrust to get you out of sticky situations. However if you push it too far, and it takes some effort, its supercritical wing will stall sharply and often asymmetrically. I'm looking forward to hearing yours and others feedback on the Harrier when the next demo comes around!