5W while browsing is already less efficiënt than my old laptop with a Zen 2 CPU (and most of the power is consumed by the display). Newer CPU's or SoC's should do quite a bit better than that.
During "light" browsing pretty much any laptop's power use is massively dominated by things that aren't the CPU, assuming there's been any attempt at enabling that use case (which doesn't always seem to be the case for many SKUs, certainly on the cheaper end).
A huge amount of Apple's competitive edge is in the "other 90%", but they don't seem to get the headlines.
