The whole problem on the infrastructure side is that the APIs are slow and you don't have exclusive access. Building the CRUD app would be a million times harder if SQL calls took 100x longer to execute and other people could randomly reach into the database and change the schema and data at will - can your basic CRUD app gracefully handle somebody shoving newlines at the end of usernames? Odds are that the first time, no, not until you put a trim() call. And then you cry in pain at needing to put trim() calls everywhere. And then you gnash your teeth at people reporting performance problems because of all the defensive checks you put in because all trust has been thrown out. And then you find out that trim() was deprecated and will now be replaced by strim() that handles Unicode a little differently, and you need to port your code before End of Life to stay compliant.
A basic CRUD application with a basic SQL database doesn't solve the problem, because you don't seem to appreciate that there already is a database - however your vendor stores configuration - and it's your job to deal with it. Adding another database on top of it would make the problem worse.