The M2 Ultra that got the best numbers that I was comparing to is not in a laptop. Regardless, you're probably right that the power consumption is significantly lower per unit time. However, is it lower per unit work done? It would be interesting to see a benchmark optimized for power. Nvidia's power consumption can usually be significantly reduced without much performance cost.

Also, the price difference between a prebuilt 4090 PC and a M2 Ultra Mac Studio can buy a lot of kilowatt hours.