That is not called flush

that is called using tranny pump to purge the ATF. Here is the difference: When say flush, that means the fluid will go over everywhere and remove settled debris with the high flow rate. What you claimed is not correct: in any case the fluid is flushing the valve body when driving by definition (just not replaced, internal cycling). When say drain and purge, the tranny is not engaged and therefore, there will be no fluid passing the valve body. The ATF is driven out by the tranny pump.
Conclusion, what you have said is not correct.