'Hound Dog' took like twelve minutes. That's not a complicated piece of work. But the rhyme scheme was difficult. Also the metric structure of the music was not easy. 'Kansas City' was maybe eight minutes, if that. Writing the early blues was spontaneous. You can hear the energy in the work.
Early on, it's good to develop the ability to write. Learning to write is a useful exercise, even if what you're writing about is not that relevant.