Your simple plan simply wouldn't work. A legislator working under those incentives would ration out job creation, delaying government hiring and projects if jobs were already set to increase in a given month. They would raise taxes however much it took to ensure that the deficit decreased. They would create make-work jobs when actual unemployment was rising.
Simplistic standards for job performance lead to "legislating to the test". You end up getting the letter of what you asked for, without the substance.