Why would you expect performace improvements? Because of JIT? There's no reason to hope that JIT would help with that much, because it's I/O-bound anyways. And function calls in PHP are pretty efficient.
Oh, come on. Did you see the benchmarks? This is CPU-bound code, like multiplying numbers 100 000 times over. This has nothing to do with your typical use case.
And, yeah, performance improvements are always advertised.
https://www.fonow.com/Images/2020/0608/9f3a0f6a4f8f2ee.png
https://www.fonow.com/Images/2020/0608/4e9d2337edd2072.png
https://www.fonow.com/Images/2020/0608/70a1c6cff23f4fc.png