@Johan_Barelds @MarvinFreeman @frescosecco bringing in a “sample of one” example of not doing speed work at all - my wife. She never trains any intervals nor tempo runs nor steady state runs nor does any speed work outs. Her regular training pace is around 5:55. Plus minus a few seconds. She runs with this 10-30km sessions. Sometimes 20km in the morning followed by 10km in the afternoon. Constant pace. She did a training marathon last year on her own and managed to do a “race” pace of 5:00 over the marathon distance without showing any signs of being really tired or trashed afterwards requiring a long recovery. No tapering either before doing this. Just out of her regular volume training.
As I said, “sample of one” story. But it shows that you don’t have to train speed to run “faster”. She attributes to the consistency she has build up over the years.