Whether fast running or slow running is better really depends on the persons movement patterns. Usually I'm just as good running slowly as fast but right now because I'm tired and sore it's easier for me to compensate and change my form to avoid weight bearing in certain ways that are sore. Make me run fast and I kick in more stabilizing muscles and don't have time to compensate.

A lot of runners in the middle of the field get worse when they run fast because it emphasizes their form faults.

A lot of people have worse walking faults than they do running because they get lazy when they are walking and don't engage their stabilizing muscles as much.