Man I wish there were really some way to settle this. It just seems like you're speaking like somebody who hasn't tried to squat with something overhead. In any event, for most sports I think yoga is pretty unneccessary, however for grappling where flexibility and isometric strength training can give you an advantage, it may be somewhat useful, I'm not denying that... but if you're looking for a healthy, happy life, serenity, ki and zen, go meditate under a waterfall. it'll be time better spent... better yet, go do overhead squats under a waterfall.
fact is there's no way for me to prove OH squats are better than yoga at improving posture, flexibility and balance. What I know, is that doing overhead squats forces you to work hard to maintain your balance, posture, and to increase your range of motion increases your functional flexibility. It's a total body movement requiring total holistic harmony in the body... how much more zen can you get? But like I said, there's no way for me to prove that it's better than yoga, and vice versa... maybe if we get a pair of twins and train them from birth in different methods... yeah! yeah that'll work. To the maturnity wing of the hospital!