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.
Report generation times:
PHP 7.4 = 67ms avg
PHP 8.0 = 66ms avg
This is getting the data from MySQL and massaging it for the templates. With Laravel's insane amount of indirection, of course.