You're absolutely right that there is no "magic ball" that will automatically strike. However different balls match up with different lane conditions and styles of delivery, so for each particular bowler there is an optimal ball choice for a given lane condition, that will make it easier to repeatedly put the ball in the pocket.
Equally as important as what board the ball is on when it first contacts the pins are the angle at which the ball hits and the phase of motion the ball is in.
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