Yes. Writing CUDA that calls CuBLAS or CUB is still writing CUDA. Lots of kernels and functions (functors, etc) are "business requirements" moreso than math libraries. It's no different than the CPU code world, there are far more CRUD apps than BLAS libraries written, and writing a CRUD app that calls a BLAS library doesn't mean you're not "writing CPU code". Someone has to write those systems of linear equations for BLAS to solve.

The world is deeper than just assembly and BLAS tuning, and you can get extremely far in CUDA just by gluing together the primitives they give. Python is popular in the AI/ML space, but far from the only way to do that.