Price taking of course prevails in the market after the equilibrium has taken place, but the question is how the equilibrium is determined beforehand, by the forces of demand and supply, which certainly remain the same before and after equilibrium (meaning that a sloping demand curve can not be horizontal at the time of equilibrium). The revision here is simply that the individual demand for the firm is the total demand equally distributed to the number of firms, because buyers certainly do not have a preference for some firms in buying the product since it is an homogeneous product. This means that the individual demand curves for the firms are sloping and not horizontal and this has tremendous implications on the economic theory and its outcomes (the equilibrium point is not at the minimum average cost, which invalidates the maximization of social welfare and the optimization of Pareto efficiency, etc).