Too much thrust on one engine in real life has a much higher bad outcome than the other way arround.
It ain't a big deal when you can trim for it, but when you are doing hand and feet stuff and then have something else go a teensy bit wrong it screws with your brain trying to adjust assymetry.
I've seen several experiments run on pilots where they got too much thrust and those that didn't shut down the offending machine often couldn't handle deteriorating situations.