Guardsmen can be more Dakka Efficent than most armies though, you could fit more Guardsmen in an area than most races, the only ones I can think of that beats them off the top of my head in a space taken to Dakka contributed ratio is Eldar, Dark Eldar and Necrons.
Because Guardsmen can field Multilasers and Multi-meltas, which are some of the best dakka contributing weapons in 40K I can think of.