My Gripen flew again today. No photos or video this time, but believe me: it was a blast! I added additional carbon spar parallel to the leading edge, approx. 1 inch away from it. That was enough to completely get rid of the "suicidal dive" tendency. Now the plane flies straight(ish) and true(ish, as far as the plane after three serious crashes can) at any speed, including full throttle dives on 4s. One downside is that the ESC becomes really hot after such flight and I need to wait at least 20 minutes before the next one... But it's nice to finally have just this kind of problems
Now I need to finish up the airframe and find some reliable camera operator...