This may be true if it the same product from the same brand with the same optics and hardware used. However; in general the nature of the components like the optical system, the heat sink, the LED chip used and the driver affects the output more than by just the wattage. A 3watt LED luminaire from one manufacturer will have a different output from a 3watt LED luminaire from another make even if the same LED chip is used. Hence using a high quality chip alone does not guarantee better performance. Note that as the wattage increases, the efficiency drops slightly. An LED driven at 3W will emit slightly less than three times the output driven at 1W.