I'm kind of hazy about where the boundaries between bona fide UML and PlantUML are, but PlantUML is in pretty common use in my world - more for sequence diagrams and state diagrams than class diagrams though. Of course PlantUML has competition from things like Mermaid, but they're all much of a muchness.

My very non-scientific impression is that tools like Rational were mostly used for drawing class diagrams and ... that just turned out not to be that useful because the tooling didn't exist to round-trip changes in the code back into the diagrams meaning the diagrams lost parity with the code rather quickly. It was sort of useful in the linear design/code/deliver world, but we're a lot more iterative now.