Not quite. Unless the system has pretty advanced power management and is using very recent technology with high density, it's unlikely that an x64 chipset will use less power than a comparably powered arm64 chipset. Not just the processor, but the smaller board is actually a power saver and allows it to generate less heat meaning both less power wasted and dissipated as heat as well as less power needed for fans to properly dissipate the heat. I've never seen a laptop use 3W at idle when considering the whole device, maybe just the CPU, but not if you include the rest of the components like RAM and disks and power supply. And especially true in a laptop that is old enough that it's being recycled. Heck, the power supply and charger alone might be using 3W at idle with full battery.
With a raspberry pi 4, the typical power usage for the 2GB RAM model is 5W under load for the whole device and about half that for idle. Add a couple of watts for the extra memory and wider bus on the 8GB model and other things can add to that, but that's mostly accurate. The pi 5 is a little more and the 3 is a little less. Of course, the efficiency of the laptop at full load might end up being better than a comparable number of raspberry pis it would take to do the same amount if work, but comparing a single pi or any other reputable arm-based, single board computer to a single laptop at idle is always going to be that way.