... there's plenty of examples of people suggesting not all cables are as good as others.
...
There are better cables and poorer cables.
The discussion of will a non-Rohloff cable work, that is a fit question, in this thread it is a diameter of cable head question.
For indexed derailleur shifters, minimizing friction is quite important for precise shifting when the indexing is in the shifter, less important for a Rohloff.
And cable composition. Last year I had a shifter fail on one of my touring bikes, cable was four years old. I was quite sure that I only bought stainless cables, but looking at the cable that failed, I think a galvanized cable snuck into my box of spares. That cable that failed looked like corrosion caused it. Two photos. A cable in bar end shifters is easily exposed to sweat in your hands that can cause corrosion.
And as Dan noted, if the head is too big, you can make it smaller. On my rando bike I have a vintage Huret friction downtube shifter for the front derailleur. That shifter uses a cable that has a head shaped quite different from current common cable heads. With a file I was able to quickly re-shape a modern cable head to fit in the Huret shifter.