You might find these posts informative:

https://chipsandcheese.com/p/arm-or-x86-isa-doesnt-matter

https://chipsandcheese.com/p/why-x86-doesnt-need-to-die

All instructions across x86 and Arm are being decoded to micro-operations, which are implementation specific. You could have an implementation which prioritizes performance, or an implementation that prioritizes power consumption, regardless of the ISA.

Decoding instructions, particularly on a modern die, doesn’t consume a significant amount of area or power, even for complicated variable length instructions.

Because it’s a take thst sounds like someone who has been reading comp.sys.mac.advocacy from 1995 when the PPC vs x86 wars were going on (and when PPC chips were already behind in performance) up through 2005 when Apple gave up and went to Intel.

You are wrong. The Snapdragon X Elite is actually a great example, unlike M1 it's performance isn't particularly great and it eats 50W under load. That makes its CPU cores a fair bit less efficient that AMDs even on the same production node. If Apple Silicon didn't exist then you might instead argue that x86-64 is more efficient than ARM.

If all that's true then why does Snapdragon have better battery life? As I said in my comment the great battery life comes from when the CPU isn't being used. It's everything else around it. That's where AMD is still significantly behind.