Instrumental Rationality

In 'The Myth of Instrumental Rationality' (2005), Raz argues that there is no distinctive form of rationality concerning means and ends. Typical ways we might fail to take the means to our ends -- e.g. weakness of will, or chronic indecision -- may just as well be implicated in our failure to adopt the right ends in the first place:

If I believe that I ought to care about how well I teach my students, but I do not, I display weakness in adopting ends. If I do care about how well I teach my students, but I fail to give them detailed comments on their essays, in spite of my belief that commenting on their essays is essential to teaching them well, I again display weakness, which this time is a manifestation of instrumental irrationality. It seems plausible, however, that the standards by which I fail are the same in both cases. (p.26)

Smith offers a compelling response though, which is that Raz doesn't seem to have addressed the distinctive capacity to "multiply out" the strength of one's ultimate desire against one's degree of belief in the efficacy of the means, to yield an appropriately weighted instrumental desire. Is there any non-instrumental analogue to this?