golang do heavy inline-ing and most of its performance comes from concurrency. Putting values on stack actually make concurrency easier.
That said, there is a proposal to do it in register: https://github.com/golang/go/issues/18597 It is challenging and not in high priority. The current priority is do more inlining.
Yes, it is. 5%-10% in the very link you posted.
> "golang do heavy inline-ing"
No, it does not. See https://github.com/golang/go/issues/17566
> "most of its performance comes from concurrency"
That's just ridiculous. They didn't write all crypto and math in assembly just for nothing. Lumping bunch of slow function calls onto several threads is not where performance magically comes from. And you are confusing concurrency and parallelism.
Could you elaborate how?