I'm having trouble understanding your interpretation of the "Nynaeve would do better still" argument.

We have two options:

1)Angreal are multipliers: So Elayne's strength gets multiplied by X, and this happens to be twice Nynaeve's strength. For Nynaeve herself, of course, multiplying her strength by X would mean access to even more of the OP.

2) Angreal are additive: there's a lot going for this, especially based on what we know about Seeds now. If so, Elayne's level+X is twice Nynaeve's strength. Obviously, Nynaeve herself would do better if X were added to her greater strength.

In neither scenario do we have to assume that angreal somehow work differently based on your strength. They either add or multiply, and they do so evenly for all channelers.