It only works that way in the simulator because the pumps are simulated by a piece of software which of course has all of them running exactly on spec which in turn means the same output pressure for each pump. As explained above that never works in real life as there is an acceptable range of output pressure. 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).
Follow the OEM guideline on that and everything will be fine.