RTX3090 is a desktop part optimized for maximum performance with a high-end desktop power supply. It isn't meaningful to compare its performance per watt with a laptop part.

Saying it offers a certain wattage worth of the desktop part means even less because it measures essentially nothing.

You would probably want to compare it to a mobile 3050 or 4050 although this still risks being a description of the different nodes more so than the actual parts.