I think that you are confused as to the meaning of the equilibrium equation.

The equilibrium equation is defined as K = product concentrations divided by the reactant concentrations...K = [product]/[reactant].

This expression does not depend on how fast the equilibrium is achieved but rather the concentrations of the products and the reactants at the time that equilibrium is achieved. Reaction rates are measured by the change in concentration of a reactant or product with respect to a change in time...it is an entirely different expression.