The weakest boy currently on my team squad has a 6 pack that he loves to show off and touch. He can barely do a few skin the cats and has a very short L-sit time. Our Muscle-man also has a 6 pack but then again he can do a front lever. A so-so L-sit time and L-hang but still FL, ridiculously long BL and straddle planche.
There's your midline stability.