In evaluating John Gray's "dismissal of perfectionism," R&D get everything right.
To use my own terms, intrapersonal virtues are (1) cognitivist, (2) (2nd-order) desire-driven, (3) externalist.
Thus, "courage is a virtue and an important human good" is truth-apt and in fact true. At the same time, there is no inherent necessary connection from realizing this truth to being motivated to cultivate courage. Everyone determines for himself which virtues to focus on and how to combine self-making with pursuit of narrow happiness. Regarding the former, R&D point out that "a person with a career in the military might require greater emphasis on the virtue of courage than would be the case for a civilian." (173) Regarding the latter, perhaps excessive concern with courage would interfere with my personal pleasure of doing philosophy, and I may need to ease up on my martial training. R&D's view "accepts emphasis and unequal weighting as central to its very identity." (179)
Gray claims that good lives considered as bundles of virtues are incommensurable. Au contraire, they are 100% commensurable, not only between themselves but even between ends belonging to narrow happiness. They become so in the process of choice:
Choosing determines all human decisions. In making his choice man chooses not only between various material things and services. All human values are offered for option.
All ends and all means, both material and ideal issues, the sublime and the base, the noble and the ignoble, are ranged in a single row and subjected to a decision which picks out one thing and sets aside another.
Nothing that men aim at or want to avoid remains outside of this arrangement into a unique scale of gradation and preference. (HA, 3)
Remember that both virtue and narrow happiness are desire-driven, so Mises' quote applies to these levels. Nature is duty-driven, and Mises took his theory too far. Nevertheless, one becomes who he wants to be and "flourishes" in the manner as per his own choice.
Innate qualities matter, too: e.g., St. Thomas writes that "by reason of a disposition in the body, some are disposed either well or ill to certain virtues... In this way one man has a natural aptitude for science, another for fortitude, another for temperance..." (ST, II-I, 63, 1)
R&D also correctly note that human beings are not omnipotent, and many ways of flourishing are simply closed to them by their inborn traits and external circumstances. A hideously ugly or miserably poor person's options in life are not pretty. Neither are a person's in locked up in prison. To reuse a quote below, "the foremost social means of making man more human is to fight poverty. Wisdom and science and the arts thrive better in a world of affluence than among needy peoples." (HA, 155)
R&D's insistence that flourishing must be "self-directed" is now also clearer. Perhaps they mean the following: suppose Smith is a doctor, but he was forced to learn the skills and to practice medicine under penalty of death for disobedience. Can we call Smith flourishing or happy? I doubt it very much. It is really silly to deny that "the absence of choice diminishes the value of human relations or the displays of excellence in technical skills, physical ability, spirit and enterprise, leadership, scholarship, creativity, or imaginativeness." (181) Presumably, we are talking about humans who acquire and use these "technical skills," etc. for their own fun and profit, not about robots. A calculator can crunch numbers way faster than I can, but I scarcely would praise it for its moral perfection.
I would demur though regarding R&D's elevation of practical wisdom to the chief and master of all virtues. If by practical wisdom we mean prudence, then all that prudence does is churns out means to arbitrarily chosen narrow-happiness ends. On the level of virtue, prudence is replaced with justice in the metaphorical sense -- as integrity; and remember that wisdom for nature, justice for virtue, and prudence for narrow happiness are human powers of judging. They therefore share a property, but their jobs are very different.