Do you think Leonardo got good enough to do the Sistine chapel by daubing a doodle or two when the mood took him?
You absolutely can and, to get good, must grind such things. Everyone knows this is true of musicianship; painting and writing are no different. (Maybe painters don't grind their technique as much nowadays as they once did, but the decline of technique in painting over time reflects that.)
As Picasso said: 'Inspiration exists, but it has to find you working'.