POSIX itself contains some interesting notes about `echo` and `printf`, e.g. from the `printf` page:
"The printf utility was added to provide functionality that has historically been provided by echo. However, due to irreconcilable differences in the various versions of echo extant, the version has few special features, leaving those to this new printf utility, which is based on one in the Ninth Edition system."
The behaviour of `echo` is especially inconsistent for escape sequences. Often, `echo -e` is used to enable escape sequences for it but this is not POSIX compliant.
For any "standards-perferring" shell scripting pages I'd thus think `printf` is the right way to present it if only to advertise that this builtin exists.
> should likely be done with external tools just because people understand "oh, awk or sed -- I know this!" instead of "what the hell is this line noise?"
I am not actually sure about this "I know this" part. I think many users of AWK only ever use it to do some sort of "access the n-th column of input" as in `echo a b c | awk '{ print $2 }'`. Similar for `sed` which is often only known and used for "replace string a by string b in input" use cases.
> If you're writing performance optimized shell, well, probably put the keyboard down
There is some difference between performance optimized and "hugely inefficient" that can make the difference between a task taking minutes vs. a few seconds. It may not seem much but shell scripts are often integrated into automated processes (think of build environments or system startup tasks) and there, seconds quickly accumulate. Whether this is relevant to your use case, only you can know.
I found this "Pure Sh Bible" to be highly interesting, but there are some places where it has some rough edges and it may not show the "best practices" for standard use cases. Still a very useful resource.