I'm not sure if the hand posture is called "ball-like" in English, but is there a difference in playing, technique and/or something else between a balled-hand and a flat one?; (most rock and synth) keyboard players have that.
I was a piano teacher for over 50 years before I retired recently, and it is my experience that no two hands are alike and no two pianists ever use exactly the same hand technique.. Success comes from finding what works for YOUR hand, and to listen to supposed 'expert' teachers lecture about 'correct' hand posture is to invite carpal tunnel syndrome.
One of the greatest pianists I ever met was Claudio Arrau. He played with absolutely flat hands, no finger curl or 'ball shape' at all. Yet he played with great control and a huge range of dynamics and total control of touch. I've met other pianists who play with perfect 'hold the ball while playing' technique who are very very good. But none of them are as good as Arrau. Find the hand posture that works for you, that gives you the best touch control and range of dynamics, and use that posture. Your hands will let you know.
Hope that helps.