It is the job of the build system, yes. In most cases the problems people want to solve with locally runnable Actions aren't the build not working, it's the whole integration of the thing; all the YAML definition, secrets, exactly what commands it runs, how it restores tools and caches (which your build system _might_ take care of but the available primitives for that in GHA are very poor), etc.

I do think it's just an awkward problem to solve though, because it essentially devolves to needing to run the entire system somewhere else, which is why every system I've seen like this ends up being trial-and-error.