I have mixed feelings about the new flight model, it's fun to try to fly with more realistic but difficult controls, but at the same time I can't do the kind of things that I did in 0.4.1
(Something I want to mention to begin with, I'm pretty new to flight games and flight mechanics, I've played a bit of War Thunder and that's basically it. I also don't have a joystick)
I feel like there can be a good game if you go either way, and that both flight models have potential.
With the older, more arcade flight model because the mouse controls are so easy and intuitive, and the planes react so well, you could add some really crazy challenges that would still be doable even to new players, because you can focus on the challenge right away and you don't have to fight the controls. You can never have played any flight game before, launch the game, and immediately start doing maneuvers, and with only a little bit of practice you can have cinematic battles and feel like a legend. This is what really keeps me playing the 0.4.1 version, the cinematic battles and being able to feel awesome. And I really want to say this again: The mouse controls in 0.4.1 are so beautifully intuitive, it takes so little time of learning to feel competent at them
With something closer to the 0.4.1 model, I think the game becomes something that anyone can try out, begin to try their hand at various challenges, and immediately get hooked on the action. It really lends itself well to situations that are unrealistic but which feel fast paced and awesome. I can imagine it being a game with crazy locations you would see in a work of science fiction, like a place where the enemies are testing an experimental fighter, or a canyon system that enemy planes and anti-air defend that leads to some underground base. I feel the controls and physics are good enough to be in a finished game, and I personally would LOVE to play that game, but of course that might not be the game you want to make.
Switching to 0.5.3.0, it feels like a completely different game. The effects feel interesting, the visual and audio feedback is a great addition. Right away, controlling the planes does feel more difficult. Having both a gamepad and a mouse, I tried both controls but as a new player the mouse controls do feel much better. However as another commenter said, I'm having to repeatedly tap the S key at times to be able to pull a bit harder, and that control feels really off, but it feels necessary to do that in many situations. However, with the gamepad I feel like I'm having to fight the controls to be able to do anything.
I will say, overcoming a more difficult challenge could theoretically be more satisfying, but getting a kill with the gamepad controls which I find very difficult felt more like sigh of relief than any kind of triumph. I was fighting with the controls a lot and at the end all I did was take out a normal enemy plane. It felt like we were on even ground and taking them out felt like "Ok, at least I'm not worse than the AI"
I will be frank, personally the combat in 0.5.3 does feel more boring. Everything happens slower than with the old model. The difficulty increased for the player, but also for the AI planes, and the AI planes tend to burn their speed and end up flying really low and really slow, making them fairly easy targets (and sometimes crash on their own). There's also times where I miss opportunities or get into bad situations and then have to spend a long time coming around for one more go, there's a lot more downtime during fights.
To compare, with the old version I feel like I'm fighting stronger enemies because the planes are faster and turn better, and they easily pull off maneuvers. In the old version you can react faster and more sharply, but also you need to react faster and more sharply because the enemy planes give you less time to relax.
A bit extra about the controls: in 0.4.1, the mouse controls are intuitive from the start, immediately feel like I have full control. The things to learn are mainly with plane's characteristics like how they behave at different speeds.
In 0.5.3, the controls are more difficult to use, mouse controls require learning to use the S key, but requires practice as holding the S key down adds too much pitch so I need to tap it instead, which often feels jerky and inaccurate. With the S key thing being as it is, to feel comfortable and have full control I feel like I would need to invest in a joystick. My suggestion would be to allow the mouse controls to pull a little bit harder, because pitching with the keyboard feels very wrong.
Now, this is a bit of a tangent, but in my head I compare these two flight models to the way Absolute Drift does driving physics, and the way Assetto Corsa does driving physics. Both are games I love.
Bear with me here, Absolute Drift gives you intuitive controls that you can master fairly quickly even with keyboard-only controls. The entire game is built around drifting, and it gives you an open world to explore and drift through, as well as various standalone tracks/circuits to drive in where you can complete set challenges. The keyboard controls are very intuitive, but the challenge is that the physics and tracks require learning in order to get better at the game. I've put dozens of hours into finishing Absolute Drift and it was a very satisfying experience. Assetto Corsa is a much more hardcore driving game, and it really requires a steering wheel, pedals and gears setup to have the ideal experience. There's a very limited campaign and the game doesn't really give you goals (there's no upgrading or buying cars or anything like that, you have access to everything from the start), and the real content of the game is the physics and the cars. I've spent over a thousand hours in Assetto Corsa, just practicing on my own because of the physics, and getting better in the game really feels like learning things that transfer to the real world. But in Assetto Corsa, a lot of the time I find myself frustrated because the reality is that it's difficult to pull off cool stunts. With the realism of the physics, you really need good equipment because the visuals and sound alone are not enough to communicate what the car is doing. Even though I have a steering wheel setup, I feel limited without VR.
Absolute Drift has unique physics, while Assetto Corsa tries to mimic the real world. So on one hand, Absolute Drift is a very unique game, but what you learn in Assetto Corsa can also transfer to other games and the real world.
Similarly, I feel that the new flight model can attract an audience that's more serious about planes and flying, and which can open new players to other flight games, but making the physics more realistic and the controls more difficult could make it harder to add satisfying challenges as the realism limits what the planes are capable of, and the difficulty limits what most players are capable of. I think it would be more difficult to give players that feeling of "Wow, I'm a legend, that was awesome!". Planes weren't made in order to be used in games, so I think going for more realism won't necessarily be better for a game.
On one hand, physics that are more realistic do open the game up for more real life maneuvers and studying of real flight mechanics. There are things in the 0.5.3 flight model that feel really good that weren't possible in 0.4.1 (For example ground effect, or using the landing gear+flaps for extra lift+drag). On the other hand, unrealistic physics can allow for things that are impossible in real life, which could turn off people who are looking for real flight mechanics, but which for others can feel awesome to pull off, because you're doing the impossible. I think finding the right balance of realism and fun is a very difficult task as it depends on what kind of game you want to make and everyone will have different preferences, but you don't have to limit yourself to real physics, you can always take liberties and add whatever you think feels good, since it's your game.
EDIT: Also in the new flight model I love how it feels like you're actually flying through air, like the slight bounce/wobble when doing sudden turns and the sound effects as you increase the angle. I feel like the new model will grow on me a bit more as I play it more.
I love your work, and look forward to future updates!