The movement of heat is proportional to the heat difference. So if you're going to move the sewage across miles of basically uninsulated pipe, you're better off taking the heat out at one end (and using it very productively, essentially all the heat removed by DWHR is used!) and then putting it back in at the other, then you are leaving it in the pipe to have 99% of it lost to the environment.

DWHR isn't very efficient in and of itself, but that is because the short contact time and small temp differences doesn't permit it to remove much heat from the waste stream. But what it doesn't remove is still there, so that for of inefficiency isn't relevant to your comment.

I think you are assuming that there won't be any heat loss wbtween the home and the plant