Someone who has hundreds or thousands of clients presumably couldn't remember every client's voice either, so no meaningful security is lost. They are approximately as secure or insecure as before

>presumably couldn't remember every client's voice either, so no meaningful security is lost

there are automated systems for this already. my bank, isp, etc. use them when you call in to skip the traditional verification steps. this fact is also highlighted in the article.

the problem is that there isnt typically a system in place for setting up or validating code words, so the advice given is not practical to implement.