How can you gain an advantage over a competitor if everyone can make the same choice? May i grind all the numbers off my irons so you can't peek and see what i play? Is that a competitive advantage for me? I personally feel all the arguments explaining or supporting the 'one-ball' rule, that i have read here, are totally bogus. The only rule that continues to make sense to me is: each ball played must conform to current list.
The closest you came to refuting the idea behind the point is that a player can have as many as 14 different drivers in his bag, essentially giving the advantage of hitting different kinds of balls but having that advantage stem from the club instead. However, it seems to me that if the player chooses to carry multiple drivers, he has to renege on other clubs he might have otherwise carried.
So, the fact that a trade-off still exists gives validity to the existence of the one-ball rule as it is. Whether it's something that should be regulated against or not does not seem to be what you're raising here.