I've never heard of Doug Portmore but your description of his work suggests that he is competent and may be worth reading.
I also recall Portmore used to think that some form of relativized consequentialism was likely to be the correct moral theory; I don't know if he still thinks that.
This seems overwhelmingly likely. Especially since the alternatives that seem plausible can be conveniently represented as instances of this. This is certainly a framework in which I evaluate all proposed systems of value. When people propose things that are not relative (such crazy things as 'total utilitarianism') then I intuitively think of that in terms of a relative consequentialist system that happens to arbitrarily assert that certain considerations must be equal.
My apologies if this doesn't deserve a Discussion post, but if this hasn't been addresed anywhere than it's clearly an important issue.
There have been many defences of consequentialism against deontology, including quite a few on this site. What I haven't seen, however, is any demonstration of how deontology is incompatible with the ideas in Elizier's Metaethics sequence- as far as I can tell, a deontologist could agree with just about everything in the Sequences.
Said deontologist would argue that, to the extent a human universial morality can exist through generalised moral instincts, said instincts tend to be deontological (as supported through scientific studies- a study of the trolley dilemna v.s the 'fat man' variant showed that people would divert the trolley but not push the fat man). This would be their argument against the consequentialist, who they could accuse of wanting a consequentialist system and ignoring the moral instincts at the basis of their own speculations.
I'm not completely sure about this, but figure it an important enough misunderstanding if I indeed misunderstood to deserve clearing up.