This is a small point but all i have time for at present.
I think you have already ironed out the problem that you ended with concerning the irony or paradox entailed in taking a capacity (potential) view of equality. On your own account it would seem that we still have 'capacity equality' if we have prooved that we are not equal but better at something than our peers, we have simply lost 'actual equality'. This is further supported by the fact that you kept refering to the ideality of the concept of equality. So i dont think that, as presented, there is a internal contradiction in the notion of equality. Rather it needs defining and distinguishing clearly. Equality is not a convention that defines itself as the negation of itself, so dont worry about that...hmm
cheers,
andy