Pareto Efficiency should not be the be-all-end-all (and only one subset of "efficiency", so your definition is only useful in isolation to Pareto Efficient). It only guarantees nothing is worse off, but that's only a relative comparison. A result of 99% of the wealth goes to 1 individual and 1% of the wealth is with everyone else is Pareto Efficient but not a good world! Efficiency can also be used amorally, e.g., Death Camps are an efficient way to kill undesirables!