Do they?

If what is being said is actually true, then amazon doesn't have any leverage at all. (again if what is being argued is true) These last mile providers might be taking a small hit to deliver amazon packages, so why deliver them at all?

If you answer is: "if they don't deliver these they won't get amazon's business." It would appear they are not getting any of amazon's profitable business (2/3 of delivers), so who cares about getting amazon's crap business?