There is a huge difference between the instruments you need to maintain control or recover from a deviation (a second AI is best for that), and the instruments you need when you have lost control in a spectacular fashion (where the AI may have toppled and a classic turn indicator is best)
I suspect most pilots are better off having instrumentation and training that prevents them from getting into an inverted spin, which includes recovery from the earlier stages of an upset, than having instrumentation and training that helps them recover from an inverted spin.
Hence the sensible backup for an electronic display where you could lose everything when the screen goes blank is an attitude indicator + airspeed, and an altimeter.
