“point is : some one who can lie on a ball and bench 32 kg dumbells will always beat the guy on the smith machine, even at his own game.”

Point is – your hypothetical trainee would never be able to build up to benching 32 kg DBs on the ball if he hadn’t already built those muscles up with more, say – conventional exercises (e.g., benches NOT on the stability ball).

Your point that someone can use more weight on a “more stable” apparatus – my point exactly. Taking your logic to an absurd extreme you could say why not have the hypothetical trainee do unilateral (one side only) dumbbell presses lying down on the ball, blindfolded, with his opposite foot up on a wobble board?

-Well I say look at a smith machine people can bench 8 reps 150 kg on a smithmachine but on a real bench they fold at 85 kg and with dumb bells they are lucky to get a combined 65 kg replace the bench with a ball and this gets even lower.
point is : some one who can lie on a ball and bench 32 kg dumbells will always beat the guy on the smith machine, even at his own game.

And its best to make sure you have isolated muscles and got the most out of them as well as doing old school compound exercises. Do seasons of each type of training and you will be amazed at how much squats , deadlifts and bench presses improve.

Mesocycle -
E-X-A-C-T-L-Y.