[lynguist]

Mike Clark, the architect of Zen says in [1] literally that ISA doesn’t matter and that it’s all about the microarchitecture.

Quote: “Although I've worked on x86 obviously for 28 years, it's just an ISA, and you can build a low-power design or a high-performance out any ISA. I mean, ISA does matter, but it's not the main component - you can change the ISA if you need some special instructions to do stuff, but really the microarchitecture is in a lot of ways independent of the ISA. There are some interesting quirks in the different ISAs, but at the end of the day, it's really about microarchitecture.”

In the end, ISA is such a small part that impacts the design of a modern high performance CPU that it is almost negligible. It is physically impacting only the decode unit, but the decode unit is only a few percent of die area. Feel free to listen to the whole interview to get a feeling.

1: https://youtu.be/3vyNzgOP5yw