It does a pretty job at certain weights/ temps /pressures with certain winds. It is an inadequate response at certain weights / temps/ pressures with certain winds. One of the great things about flying is that the variables are so many that judgement is often required to determine the best action.
Don't worry whether or not you were right or wrong, worry whether or not you can learn something from the flight and become better. Even if that is just learning why the Captain made a different assessment of the energy state than you did.