Part of the reason foot closure isn't seen so much at high levels is that it takes extreme expertise to round out the bottom of the downswing when lowering from foot closure. How often have you seen a couple start their waltz with a natural into some derivative of a spin turn, but the lady can't commence to rise as she passes over her forwards step 4 because the couple is either still lowering, having not rounded the bottom corner of the swing, or has fallen off the step and gotten their legs to wide, so she's stuck between her feet with no power.