If anyone complained about the FM in 4.0+ it was because he was too used to the earlier FMs. I started Il-2 with FB and AEP, and it really doesn't capture the feeling of flight like our current system.
Regarding SOW, Luthier has mentioned that he had to re-learn everything when flying the Spit, and that gunnery was especially difficult. Sounds promising.
And lastly, regarding the 109 handling: The author mentions that the Bf-109 E could roll when slats were deployed. I think this had to do with one coming out before the other. If we consider that these are designed to increase air flow over the wing, and therefore increase lift, at low speeds and high angles of attack, then this is not surprising. I would really like to see this and other details like it modeled, based on difficulty settings. For example, Soviet crates which have varying weight from plane to plane, optional radio or even canopy, and reliability issues such as de-laminating wing panels (sometimes out of player control for a campaign). That should put La-noobs in their place
(only joking of course, by the time La-7s were around most manufacturing problems were resolved

).
Another thing to touch upon is power settings. Really, you can not run at full power for more than a few minutes, or you will damage the engine, or at least dramatically shorten its service life. In Il-2, you can cruise around all day at 100%, but I think this is already being addressed in SOW given what has already been shown to us.