

Battery charging circuits don’t operate continuously when the device is charged. Pi also still needs a PSU, typically a phone charger, and for a server application would need an SSD or HDD in most cases. SD cards have lower performance, write endurance, and capacity after all. A single raspberry pi couldn’t match even a somewhat old laptop in performance. In terms of actual efficiency (performance per watt) Pis don’t do that well as they are using cheap processors made using old core designs and even older process nodes. Even the latest Pi 5 uses a 16nm process node with a core design from 2018. A 10 year old laptop might have 14nm process node which would be better. This means that a laptop would have more performance, so even if it had more power consumption at peak it could still end up with significantly better performance per watt, and that extra performance allows it to idle more often as it spends less time processing requests.
Of course the ultimate in performance per watt is always going to be a modern high power server or an Apple Silicon device. Mini PCs can also do well for home use, and are much lower power so better suited to less demanding usage, and have the best performance per watt for consumer devices. The M4 Mac Mini for example is pretty much best in class in performance per watt, and low power consumption at the same time.
So do Raspberry Pi?