Rosario is not a good coach IMO. They publish all their training online, and he often has guys doing dumb and pointless workouts like 30x400 at 10k pace
30 x 400m is not a dumb and pointless workout as long as the main purpose is to run at lactic threshold. The rests in that kind of workout will not be so long so it gives a good stimuli to the body at LT-pace. The Portuguese very good marathoners sometimes used to do even 40-50 x 400s this way.