finding the shortest path in a graph

The distinction I find useful is between "computer science", perhaps better called "the study of the characteristics and limitations of algorithmic computations"; and "software engineering", which is supposed to be "the systematic application of science, mathematics, technology and engineering principles to the analysis, development and maintenance of software systems, with the aim of transforming software development from an ad hoc craft to a repeatable, quantifiable and manageable process" (according to one definition from a university).

The former strikes me as a healthy discipline, the latter much less so.

to be made fast and still be good enough

Well, assume that's the goal. When people take decisions which result in both "slow" and "not good enough", we would say that they are irrational. In practice, "quick and dirty" code often results in being actually "slow and dirty".

The methods we now use to build software are by and large quite irrational.

The aim of "software engineering" could be better described as "instrumentally rational approaches to creating software in the pursuit of a variety of (arbitrary, i.e. not necessarily epistemically rational) goals".

The problem, then, is that software engineering has failed to offer approaches that are instrumentally rational in that sense: it gives advice that doesn't work, based on opinion that turns out not to be backed by good empirical evidence but on academic politics and ideology.