"Waterfall" is not a development process. But plenty of the processes that give space for planning, also give space for QA. So surely agile, in the broad sense of development processes, is relevant to the comparison.
Being an actual process and being slow and bad are not opposites of each other. Literally, every recent software engineering book has a section on the "Waterfall Process". Nobody claims waterfall is good, but it is a software development process.
