My career started in the 2000s. Oracle was already a bit of a cancer then. It was Oracle or MS SQL for "real" databases. There were technologies that had been exciting in the 90s but were already choked out by the duopoly like InterBase and Foxpro.

There were "greybeard" DBAs who were all smug Oracle guys.

My impression then was that Oracle didn't invent anything but had dominated through better funding and ruthless expansion. Administrating a Oracle DB at scale was really hard but that created armys of loyal DBAs protecting their hard-won skills.