Orgs using fewer DB engines makes sense. Supporting one as a vendor is hard when customers need your product to work on multiple versions and cloud flavours which have many differences. ( (SQL Server 2017, 19, 22) * (Azure SQLDB, MI, Fabric, RDS, Cloud SQL and on-prem) ) = Lots!

Love DB migration failures resend.com/blog/incident-rep…

why????

The best app is no app

That sounds ok as long as you can stub the response of the code calling the SP so that you don't require a SQL instance when testing. If not, testing will likely be slow and complicated. Integration testing will be important here too

If business logic (BL) is in it's own layer that doesn't depend on anything except your domain specific objects, you can _easily_ change and add things that depend on the BL like your database, APIs, etc. Easier said than done but almost impossible with BL in the DB inside SPs.