The single-arm pullover amplifies core activation to the extreme. There's an anti-rotation and rotary stability component that isn't present during the bilateral or isolateral versions of the pullover.
Add in the leg raise hold as I have my NFL athlete Fernando Velasco doing in this video and you'll find this to be one of the most challenging core exercises there is. It's also an incredible movement for exposing and addressing imbalances throughout the kinetic chain.
Dr. Ken Kinakin, much like Dr. Mike Leahy, knows your pain. In fact, he's made a living off of it. The doc is one of the best in the world at devising training protocols to help make you injury-proof. Yeah, he likes bodybuilding and powerlifting routines, too, but when it comes to figuring out how to fix what ails ya', he's one of the best.