That's not really a fair question at all because: Yes they can reach 3 watts per diode because they are 3 watt diodes but the drivers won't allow it. Most importantly, if the drivers did kick out enough juice then the cost to cool the diode would up the energy intake, raise the price or both.
My point was that there IS a difference in the size of diode that can justify labeling a panel by it's diode size combined vs power draw. A 140 watt actual wattage consumed panel using 3 watt diodes has much better penetration and growing ability vs the same wattage panel composed of 1 watt diodes so labeling your panel by actual wattage don't do much for a consumer making a decision either.
So what does help a consumer? Well IMO having both the diode capacity total wattage & the wattage consumed, because 1 without the other is meaningless.