> There's no native Unix equivalent to frequencies, this sort | uniq -c is the closest we can get. Not only is it less performant (it has to collect the full input into memory before continuing), but it ties aggregation to ordering.

One of the core features of the Unix command-line is that it is user-extensible. If there's no "native" command equivalent to frequencies, you can write your own, and it will be given the same first-class treatment as any other binary in your PATH. This is entirely in keeping with the Unix philosophy of simple implementations.