I recently had to remove Windows completely from a few years old laptop with an 12th gen cpu and a Intel Iris / GeForce RTX 3060 Mobile combo because it was running very hot (90c+) and the fans were constantly running. Running Linux, I have no issues. I just double checked since I had not for several months, and temperature is 40c lower on my lap than it was propped up on a book for maximum airflow. Full disclaimer, I would have done this anyways, but the process was sped up because my wife was extremely annoyed with the noise my new-to-me computer was making, and it was cooking the components.
I have learned to start with the OS when things are tangibly off, and only eventually come back to point the finger at my hardware.
Though it has definitely been getting better in the last 1.5 years using Asahi Linux and in some areas it is a better experience than most laptops running Linux (sound, cameras, etc.). The developers even wrote a full fledged physical speaker simulator just so it could be efficiently driven over its "naive" limits.
My guess is ARM64 is a few percent more efficient, something AMD has claimed in the past. They're now saying it would be identical, which is probably not far from the truth.
The simple fact of the matter is that the ISA is only a small part of how long your battery lasts. If you're gaming or rendering or compiling it's going to matter a lot, and Apple battery life is pretty comparable in these scenarios. If you're reading, writing, browsing or watching then your cores are going to be mostly idle, so the only thing the ISA influences won't even have a current running through it.
I've tried a Ryzen 7 that had a similar efficiency to an M1 according to some tests, and that thing ran hot like crazy. Its just marketing bullshit to me now..