What Snapper says
Don't get me wrong, the game is still fun to fly, but it can not be called realistic or a 'sim' until they fix the performance issues and untile they incorporate things like radiator drag, open canopy drag, sort out the weight issues, high alt flight behaviour etc. The problem is not -25% for every plane, they simply got the FMs wrong. Some more, some less, but we're currently not flying BoB aircraft.
Regarding the Bf 109E stall, I had this problem when I first applied the patch, but then I did the trick described by DavidRed (deleting the confuser.ini file), reseting my controls settings effectively - voila, no violent stalls, still unstable and different rudder response to what it was prior to the alpha patch. I feel it has something to do with the input sensitivity changes (same with Spitfire throttle or all rudder axes). It just took me a while to get used to it. I will fly more in the coming days and I will report back if I am wrong.