But games with difficulty modes always are. It happens naturally, developers and testers are just doing their job after all, to them it is easier to always test things on the easiest difficulty setting so that setting is what gets most development time. Solo developers might be able to work around this, but in a large team this will always happen. High level of polish comes when everyone is forced to run through the content, since then everyone will provide feedback and solutions to problems will be found. If a part is too hard or too tedious people will complain and the part will be made easier or changed, this wont happen if you enable developers or testers to run easier modes.