I don't think Sobers being number 1 is unfair at all.
Yes, Bradman is, was and is likely to ever shall be the greatest batsman. However, Sobers batting is hardly poor and compares very well to everyone bar Bradman. His bowling in particular sets him apart from Bradman. As the question is greatest cricketer, not greatest batsman, I don't think Sobers is far off.
As I already said, I'd have put Marshall at number 1 myself. I would have considered overall contribution to the game, and Marshall's off-field role in young player development, coupled with him being (to me) the number 1 bowler, his underrated batting, the entertainment factor et. al.
For those who deliberately went out of their way to not include Bradman - well, I'm sad you decided to waste Smiley & NUFAN's time.