First, it seems to me that this is mainly a debate over the definition of instrumental rationality. And I suspect the reason people want to have this debate is so they can figure out whether they count as especially "instrumentally rational" or not.
The simplest definition of "instrumentally rational" I can think of is "a person is instrumentally rational to the extent they are good at acting to achieve their goals". Thus somebody with akrasia would not qualify as a very instrumentally rational under this simple definition. Your definition amounts to drawing the boundary of agency differently so it doesn't end at the person's body, but slices through their brain between them and their akrasia. I don't much like this definition because it seems as though knowing what the best thing to do (as opposed to doing it) should be in the domain of epistemic rationality, not instrumental rationality.
I would prefer to draw the line at the person's entire brain, so that someone who had a better intuitive understanding of probability theory might qualify as being more instrumentally rational, but an especially wealthy or strong person would not, even if those characteristics made them better at acting to achieve their goals.
Related thread on word usage: http://lesswrong.com/lw/96n/meta_rational_vs_optimized/
The post actually seems to equivocate between epistemic and instrumental rationality - note the use of "rational beliefs" and "rational choices" in the same sentence.
I think it's easy to defend a much weaker version of the thesis, that instrumental rationality maximizes expected utility, not utility of results.
Someone who claims to have read "the vast majority" of the Sequences recently misinterpreted me to be saying that I "accept 'life success' as an important metric for rationality." This may be a common confusion among LessWrongers due to statements like "rationality is systematized winning" and "be careful… any time you find yourself defining the [rationalist] as someone other than the agent who is currently smiling from on top of a giant heap of utility."
So, let me explain why Actual Winning isn't a strong measure of rationality.
In cognitive science, the "Standard Picture" (Stein 1996) of rationality is that rationality is a normative concept defined by logic, Bayesian probability theory, and Bayesian decision theory (aka "rational choice theory"). (Also see the standard textbooks on judgment and decision-making, e.g. Thinking and Deciding and Rational Choice in an Uncertain World.) Oaksford & Chater (2012) explain:
Is it meaningful to attempt to develop a general theory of rationality at all? We might tentatively suggest that it is a prima facie sign of irrationality to believe in alien abduction, or to will a sports team to win in order to increase their chance of victory. But these views or actions might be entirely rational, given suitably nonstandard background beliefs about other alien activity and the general efficacy of psychic powers. Irrationality may, though, be ascribed if there is a clash between a particular belief or behavior and such background assumptions. Thus, a thorough-going physicalist may, perhaps, be accused of irrationality if she simultaneously believes in psychic powers. A theory of rationality cannot, therefore, be viewed as clarifying either what people should believe or how people should act—but it can determine whether beliefs and behaviors are compatible. Similarly, a theory of rational choice cannot determine whether it is rational to smoke or to exercise daily; but it might clarify whether a particular choice is compatible with other beliefs and choices.
From this viewpoint, normative theories can be viewed as clarifying conditions of consistency… Logic can be viewed as studying the notion of consistency over beliefs. Probability… studies consistency over degrees of belief. Rational choice theory studies the consistency of beliefs and values with choices.
Thus, one could have highly rational beliefs and make highly rational choices and still fail to win due to akrasia, lack of resources, lack of intelligence, and so on. Like intelligence and money, rationality is only a ceteris paribus predictor of success.
So while it's empirically true (Stanovich 2010) that rationality is a predictor of life success, it's a weak one. (At least, it's a weak predictor of success at the levels of human rationality we are capable of training today.) If you want to more reliably achieve life success, I recommend inheriting a billion dollars or, failing that, being born+raised to have an excellent work ethic and low akrasia.
The reason you should "be careful… any time you find yourself defining the [rationalist] as someone other than the agent who is currently smiling from on top of a giant heap of utility" is because you should "never end up envying someone else's mere choices." You are still allowed to envy their resources, intelligence, work ethic, mastery over akrasia, and other predictors of success.