>>These conclusions presume that the mixed set is optimized by a combination of experimentation, research (including exploration of what cable types other users of the same components have found to be optimal for use with each of those components), and development of as good an understanding as possible of the technical factors that are involved.<<
Sure, that's where the case must go, but for how long does the choosing last and across what universe of choice does it roam?
The problem with choosing multiple different cables from multiple different vendors is the evaluation process and the prospect for confidence in its results.
Let me come back to another silly car tire analogy to enhance my point about evaluation: Trying to assess the sonic characteristics of a single cable by inserting it into an existing system strikes me as being about as cogent as assessing Bridgestone Blizzak snow tires by mounting one on a car otherwise shod with Pirelli Sottozeroes. Sure, something will be different, but not in a usefully describable way to anyone interested in Blizzaks.
Given possible combinations within a mixed set, when does combination exploration stop? Given an indefinite amount of time and a universe of choice of all cables (to be generous say that is cut in half by recommendations and research), then it may be possible that a mixed set selection could be better in a specific system than a loom chosen for that system. But likely better? I don't see how that conclusion arrives.
(At the end of the day, I suspect that a person who chooses from a set of looms is likely more confident of their choice than someone picking a combination set from a multitude of vendors. But that's just my opinion.)
I believe the case can be pleaded based on some personal experience, but I do not believe it can be established by an argument appealing to the multiply varied electrical characteristics of the wide world of components and their interactions.
A different theory has some (not all) people choosing mixed sets of cables for a couple different reasons that have nothing to do with a belief that mixed sets are somehow more likely to be better: a) they pick individual cables with different colorations because they want to "tune" the sound of a system using or b) they cannot afford to buy a complete loom all at once.
For the OP (perhaps long gone?) here is a
link to an article that tries to lay out the loom case. Yes, the article was sponsored by Nordost.