He is correct, of course. The magneto has had it’s place in history and for specific reasons, but the reliability issue is long since died with the advent of modern electronic control systems. My 2002 Dodge Ram has a similar setup to the aviation engine, in that, each cylinder has a coil of its own mounted atop the spark plug, at the end of the plug wire. This allows low system voltage to be supplied to the coils and cutoff via electronic computer control to fire the plug. The aviation engines usually have two spark plugs per cylinder for redundancy and to allow two different flame fronts to be initiated simultaneously to reduce knock. Each had it own magneto. This old system could be replaced easily with a system similar to whats used by my old Dodge pickup...............
I would bet that this is an FAA ossified technology issue. The FAA is allows innovation in aircraft design to move forward at only glacial speed, especially for general aviation. The hoops that must be jumped through are so expensive and time consuming that small aircraft manufacturers simply cannot afford them.