The configuring/deploying/monitoring the DB infrastructure DBAs are production DBAs. The ones tuning query performance are developer DBAs. If you put the large queries in stored procedures instead of the application, they can be easily touched and improved by DBAs.

No need of DBAs if your database is up to a few GB, you cannot live without DBAs if you exceed 100GB. I have several hundred SQL servers with databases exceeding 1 TB, on average several hundreds of GB each. This is where performance tuning is essential.