It isn't that difficult to optimize relational SQL databases. I've dealt with databases with billions of rows in hundreds of tables and the company's initial thought was to flatten the schema due to perf. complaints.

We got queries down from 30+ seconds to 5 ms simply by properly indexing, defragmentation, analyzing query plans, SQL Stored Procedures, etc.

I see a lot of complaints from developers claiming they have to join a "million row table to million row table" and reports are slow, and this gets blamed on the DB. These should not be slow outside of how much bandwidth is being pushed over the wire, which is often exactly what the problem is. They just didn't see it.