Of course it's reasonable to use cat on one file. Why should it work for all 𝑛≥2 files, but suddenly fail at 𝑛=1? Despite the dismissive tone of the article

Of course it's reasonable to use cat on one file. Why should it work for all 𝑛≥2 files, but suddenly fail at 𝑛=1? Despite the dismissive tone of the article you linked, if the overhead of one single process was remotely relevant, shell wouldn't be a good fit.