There's an argument to be made that if a backpedalling scrum can stay straight and square for more than 5 metres then the attacking team is called to use it and no penalties can be called at that point.
It would still allow pushover tries from 5m scrums, allow teams to get an advantage from having a dominant scrum but remove the ability of teams to gain a penalty advantage from their scrums and keep playing each time.
It is a big advantage where you can effectively milk a penalty advantage whilst still having the ability to keep the ball and play under advantage. It is worth significantly more than just getting awarded a penalty.
It would still allow pushover tries from 5m scrums, allow teams to get an advantage from having a dominant scrum but remove the ability of teams to gain a penalty advantage from their scrums and keep playing each time.
It is a big advantage where you can effectively milk a penalty advantage whilst still having the ability to keep the ball and play under advantage. It is worth significantly more than just getting awarded a penalty.