They have comparable TFLOPs range.
1080 mobile is way faster than 1060 (60-90% faster [^1]) and definitely ahead of M1 by a large factor.
[1]: https://gpu.userbenchmark.com/Compare/Nvidia-GTX-1080-Mobile...
M1 GPU isn't really that powerful, it's comparable to nVidia 760 (from 2013). The M1's Neural Engine does have more kick of course, but the GPU otherwise is nothing superb (other than marketing).
A more modern comparison with mobility GPU would be GTX 1050 Ti mobility, which is around 10-20% faster than 760: https://gpu.userbenchmark.com/Compare/Nvidia-GTX-760-vs-Nvid...
Even still, 1050 ti uses up around 75w of power (2016) and 760 has a TDP of 170W (2013) while M1 GPU is much less than 10W (at full load, it peaks at 16w in Mac mini for the entire SoC, not just GPU).
It would be interesting to see what Apple does when it scales it up to 75w or more for their own custom desktop GPUs which is rumored in development. However, separate desktop GPU does lose the benefits of UMA that makes M1 fast.
The nice thing about the desktop is that it can just train for days and I don't need to work about using it for other things, losing time moving locations, etc. It's also still probably cheaper than the m1 laptop, even with a nicer gpu than what you can find in the trash.
From Geekbench it also looks like the m1 gpu is about 1/4-1/3 as powerful as a 1080.
The m1 may benefit from faster ram and shared memory though.
Apple states that the neural engine is able to do about 11 trillion operations per second (but oddly enough, they don’t report tflops).
Apple's dedicated ML hardware is probably quite good, but we don't have any way to know how good without doing math on die size + power draw and running benchmarks.