This is clear only when you compare against an obsolete Intel which is known to be throttling power hog.
The difference might be way smaller or non-existent once we see some comparisons with latest AMD offerings (especially when we have also CPUs with comparable process).
Yeah, Anandtech's dive revealed some interesting benchmark results - such as the Zen 2 4200U part being quite close in both performance and power consumption (a little higher) to the M1 in heavily multithreaded tasks, but getting stomped in both aspects in single-threaded ones.
The M1 isn't a tiny power-sipping mobile part - it sucks power down just like AMD's 15W TDP CPUs do. The efficiency gains Apple are getting here are likely to be the result of several factors, only one of which are the CPU cores themselves.
The difference might be way smaller or non-existent once we see some comparisons with latest AMD offerings (especially when we have also CPUs with comparable process).