thing is, the charge is like a last hurrah that is unlikely to achieve much (except maybe taking out those 2 bloodthirsty generals on the wings)
the Qin plan is not to defeat the Zhao army by strength of arms, but to last long enough to engineer a "palace coup", where the King will come to distrust the Zhao supreme general for sedition, and replace him with a lesser gifted-one.
that's when Qin will wipe the Zhao to the ground (again)