Simply keeping all pumps on and opening the crossfeed valve is therefore pretty stupid as the result will be kinda random, not controlled.
There were a few pilots who used the same "technique" in the simulator in my outfit. They were reminded about the error of their ways and in some stubborn cases failed and send back for retraining (a failed check will only lead to retraining and recheck, nothing more no matter how long it takes).
Not as stupid as flaming out with fuel available because your company refuses you to fly an approach with the crossfeed open with all pumps running.