Really well put, I'm envious of your grasp, and lucidity and parsimony of argument here. I think your point about loss of control being a fact is a very apt one.
I think that point however can be extended to a great degree and this is a problem for criminal justice - many people are not really fully choosing the bad things they do, and if they are, then perhaps not to the same degree as others. Total free choice, full autonomy, is a bit of a judicial fiction. But the fiction serves a very important purpose. Deterrence, in the interests of the kind of public safety which is prior to nearly everything else we value. That's why a looter in a riot taking a bottle of milk, is very different to an ordinary thief of a bottle of milk. The judge has to ask "but for my judgement, what future harms will be accepted or deterred". Yes he uses the language of desert - partly misleadingly: the wickedness of taking the bottle of milk in a riot may seem worse than the ordinary taking, but not so much as to justify the additional sentence on purely desert-based grounds. The underlying rationale for the additional sentence in that circumstance and that of the road rager is (if we accept that the road rager may have lost it, which is actually opening himself to a Broadmoor sentence, but let's accept he's just an 'everyday' automaton) pure utility, i.e. public welfare.
There is actually an additional desert-based take-home for the public, which is 'don't put yourself in a position where this wrong could happen'. I accept that might not justify sentences which follow, on purely desert grounds.
It's tricky because another theory of wrongs (that of Immanuel Kant), has it that simply acting on maxims which, if everyone acted on them, would destroy the social order, is itself a wrong: e.g. "when I see a riot I will join in the disorder", or "when I am angry I will lose control". Of course in your well-made example, it is questionable whether the person losing control acts on a maxim at all. However it is surely clearer that long sentences for unhinged violence, signal to the public that they should 'stay out of trouble' generally, and avoid the risk of losing control. Although I accept your point that in huge numbers of real situations (your road rage example is better than the rioting imho, sorry guys) a lack of perfect and informed choice seems real and this is a serious problem for the fairness and proportionality of sentencing.