Very interesting discussion. I think something that (understandably, as your thesis here is narrow) should be considered is how ethical theories outside of utilitarianism and deontology should be considered. Although you provided a fairly strong argument against deontology, there was no argument for uniquely utilitarianism as many of the intuition you had against deontology could also apply to most other ethical theories. Perhaps a virtue ethical, care ethical, or communitarian approach could accommodate for the short comings of deontology as well as (or maybe better than!) utilitarianism.
Thank you for the post!
Correct me if Im wrong, but it doesnt seem like virtue ethics or care ethics relies on side constraints -- they seem uniquely deontic. Im not sure that rejecting deontology implies a form consequentialism as virtue or feminist ethics are still viable at that point.