The problem is that pulling backward from the center of the board actually requires more effort force than it would to simply push down on the back side. So yeah, you are transferring energy to the center of the board, but at the center of the board it can't be used as efficiently and could be considered wasted energy. Transferring energy straight the the back side of the board sends most of the energy in that direction and requires less effort force. So you're not "skipping a force redirection", you're actually adding one: 1.) pushing back to 2.) pull up. There is one-less force vector with a traditional highback: 1.) pushing back.
That's my theory of why Flow bindings are inefficient for making heel-side turns.