It seems to me that the heat of reaction nullifies the concept of the heat of formation. The heat of formation is the enthalpy change associated with formation of 1 mole of a compound from its constituent elements in its standard state. The heat of reaction is the enthalpy change that occur when stoichiometric quantities of reactants at some T and p react to form products at the same T and p. Well, if you define T and p, then the heat of reaction should be the same as the heat of formation, right? Therefore, the standard heat of formation and standard heat of reaction is the same, provided that one mole of the compound is formed. However, the heat of reaction gives flexibility in that its not limited to standard state, and also it can be for any amount of moles formed, as long as the stoichiometric quantity is correct.