I doubt the instruction set is the only (or even the main) advantage M1 has. Apple just has been hiring some of the best talent in the field for a long time now that have been working on their phone/tablet chips and now used their talents on the M1.

There is a lot you can do to improve a CPU without changing the instruction set or manufacturing process just by doing a better job at designing the CPU itself. (look at Ryzen 5000 series with 15 to 20% IPC gain over the 3000/4000 series while staying on the same manufacturing process for example)

Basically there is a lot to gain just by doing a better design on the CPU itself. Also faster CPUs/GPUs allows one to build faster CPUs/GPUs just because as with more compute around you can run simulations faster/with more accuracy thus allowing faster development/better designs.