This reminds me of a part of Zombie Sequence, specifically the Giant Lookup Table. Yes, you can approximate consequentialism by a sufficiently complex set of deontological rules, but the question is: Where did those rules come from? What process generated them?
If we somehow wouldn't have any consequentialist intuitions, what is that probability that we would invent a "don't murder" deontological rule, instead of all the possible alternatives? Actually, why would we even feel a need for having any rules?
Deontological rules seem analogical to a lookup table. They are precomputed answers to ethical questions. Yes, they may be correct. Yes, using them is probably much faster than trying to compute them from scratch. But the reason why we have these deontological rules instead of some other deontological rules is partly consequentialism and partly historical accidents.
Where did those rules come from? What process generated them?
Where did your utility function come from? What process generated it?
I have previously been saying things like "consequentialism is obviously correct". But it occurred to me that this was gibberish this morning.
I maintain that, for any consequentialist goal, you can construct a set of deontological rules which will achieve approximately the same outcome. The more fidelity you require, the more rules you'll have to make (so of course it's only isomorphic in the limit).
Similarly, for any given deontological system, one can construct a set of virtues which will cause the same behavior (e.g., "don't murder" becomes "it is virtuous to be the sort of person who doesn't murder")
The opposite is also true. Given a virtue ethics system, one can construct deontological rules which will cause the same things to happen. And given deontological rules, it's easy to get a consequentialist system by predicting what the rules will cause to happen and then calling that your desired outcome.
Given that you can phrase your desired (outcome, virtues, rules) in any system, it's really silly to argue about which system is the "correct" one.
Instead, recognize that some ethical systems are better for some tasks. Want to compute actions given limited computation? Better use deontological rules or maybe virtue ethics. Want to plan a society that makes everyone "happy" for some value of "happy"? Better use consequentialist reasoning.
Last thought: none of the three frameworks actually gives any insight into morality. Deontology leaves the question of "what rules?", virtue ethics leaves the question of "what virtues?", and consequentialism leaves the question of "what outcome?". The hard part of ethics is answering those questions.
(ducks before accusations of misusing "isomorphic")