Ah, the age old question.
UX writing isn't a new thing, but its gained traction in the last few years. While many companies still don't have a dedicated UX writer on their team, more and more are starting to see that the investment might be worth it. The argument against? The UX designers can just write the copy.
It can be a difficult argument to refute, because writing is design. It's a huge part of the process and end result. If you've read my blog before, you'll know that UX writing isn't just polishing copy. It's about information architecture, hierarchy, terminology, accessibility, localization, consistency, tone, voice...
...and on and on. Most of the designers I've worked with had never worked with a UX writer before, and though they were surprised to know such a specialised job exists, most felt that there had been something missing beforehand. I won't go into the benefits of good UX writing here; there are plenty of articles (on my own blog and off) that argue why it's important.
So let's take that as a given: yes, UX writing matters. But can't the designers just do it?
The TL;DR answer is kinda.
My recent strategy is to teach designers how to become better writers, while knowing that it's not and will never be their main focus. This has worked well for several reasons:
Better writing means better design - If designers have at least a rudimentary understanding of UX writing, the structure and story of their design will reflect that. I flatter myself to hope that the tips and tricks they learn from me will be helpful down the road in their career.
Content reviews become more productive - Once designers know the big mistakes to avoid, content reviews and meetings can focus on deeper questions. It's a waste of everyone's time if I have to fix the same problem on every flow. If the basics are already there, my effort can go towards refining the copy.
I'm constantly challenged - I don't believe in gatekeeping knowledge. My specialisation shouldn't be seen as this magical fix that happens behind the curtain. If my process is out in the open, designers can see that, hey, this isn't too hard: once you start thinking about content's role in design, it's easy to avoid most of mistakes. Since I challenge myself to be open about my process and decisions, I have to give my best work: meaning I can stand by my decisions and defend what I think is best.
If you head a design team, a writer can provide extra support and refinement to your product. If that's not in your budget, by all means provide some training to the existing designers; encourage them to read some UX writing books, complete daily challenges, or attend some workshops. But you get what you put in; having a dedicated writer on the team will insure that someone's responsible and passionate about your product's content, and moving everyone in the right direction.