i don't know, cruise ships seem to do just fine w/o tugs. they come and go and turn 180 deg and more leaving the port of miami and geiranger norway. and they don't need tugs to dock or leave the dock. they use thrusters and can move sideways. container ships are another story. they don't have thrusters and need tugs to maneuver in tight places and for docking.
The fact that you said a 767 is small and that airplanes can’t move backwards on their own shows how much knowledge is lacking here.
The example of “smaller planes like the 767 and Bombardier” seems to suggest a lack of knowledge of the broader selection of commercial aircraft models.
Your joking a plane can push it self back they have THRUST REVERSERS HOW DO YOU THINK THEY SLOW DOWN ON LANDING !!!
Airlines should just hire bodybuilders to move them , it would be a green solution
If a 767 is your idea of small then I would hate to see what large planes would be classified as according to you.