That's not really an accurate depiction. All planes constantly change the control settings required during different flight conditions in order to maintain leve

That's not really an accurate depiction. All planes constantly change the control settings required during different flight conditions in order to maintain level flight, often with software. Different speeds, flaps, weather conditions all require different trims to those control settings. If your plane gets new flight characteristics through a design change, the configurations your training told you should work will probably not work anymore. What Boeing did was hide the change in flight characteristics caused by the new engines using software, so pilots didn't need to retrain, and they borked the implementation.