Thanks Darius! I agree that this is probably one of the strongest arguments against my model; what I gather from your reply is that we don’t need other moral theories since everything can already be explained by utilitarianism.
I agree with you that some sort of a consequentalist moral theory probably underpins the other moral theories (why should we be virtuous if it didn’t have a good consequences?). However—I think this is not giving enough credit to those theories, since if their moral prescriptions are correct according to utilitarianism, the theories themselves should be considered correct.
To take another example from physics: of course we know that quantum mechanics is more fundamental than classical mechanics (classical mechanics is the limit of quantum mechanics at large scales). This doesn’t mean that people consider classical mechanics “just quantum mechanics with some heuristics”—it is considered to be a field in its own right. The reason is that at the physical scale at which classical mechanics becomes useful, quantum mechanics becomes too cumbersome to use. Students who are asked to calculate the motion of a ball down an inclined plane don’t start with quantum mechanics, they go directly to classical mechanics, which is infinitely more useful for solving problems at that scale.
My argument is that at certain scales, virtue ethics and deontology should be considered emergent moral theories, either from utilitarianism or some other theory. But this doesn’t mean that they are “just utilitarianism with some heuristics”. They should be studied and practiced in their own rights, since the insights they give are more useful for how to live our daily lives or how we should structure a society. If utilitarianism + heuristics is just virtue ethics at some scale, why not just call it virtue ethics and use utilitarianism to justify why it is correct at that scale?