The best programmers can move fluidly between programming languages, using whichever one makes the most sense for the current problem. I mean, sure, you can use a language for a problem it wasn’t designed for, such as writing a boot loader in PHP, but it’s a lot of work and most programmers would save themselves the torment and choose a better fit. But the ability to pick a suitable tool for their current job is something that all senior programmers have in common.
It’s exactly the same with copywriters.
Copywriters know how to use the right words, format, organisation and other tricks to get their point across and make their writing interesting enough that the reader will get to the end. The right technique changes with the audience and the objective.
Just like programming, writing is all about ideas. Yes, you express those ideas with words the same way that you express algorithms with language syntax, but you start with ideas. And the capacity for thinking up new ideas can be applied to any situation. Ideas are strategy, words are execution.
Being good with words is basically table stakes — it’s a necessary but not sufficient condition for being a good writer.
So, when you’re looking to hire a copywriter you need to find someone that writes the way you like. Though perhaps most importantly, you need to like the way that they think.