It's a difficult thing to generalise but if you have a pretty large or complex application and DBA (or several) then it does sometimes pay to have your DBAs write the SQL because it's a different enough paradigm from normal backend development that not all backend developers are skilled at writing perfomant SQL. However few applications are that complex, not all businesses can afford a dedicated DBA team, and there are clearly a lot of very talented developers who can turn their hand to multiple different stacks. So it's a difficult thing to generalise.