As endurance athletes do most of their traing in th elower end of the intencity range with some high intensity. I would guess that steps can equal LISS or even HIIT if enough steps are done. When i look at peole that have lived the longest as into their 90's or hundreds i steps being by far more what they did then anything else. They can burn as many caloories if enough are done. The difference in walking a mile and running a mie in calories burned is not huge. If someone has shorter term goals then something other then steps may be needed.