That is not a flaw but simply benchmarking something else. "This would be the performance if you changed all those settings, fixed these errors etc." might be a nice academic exercise, but "this is the performance you get out of the box" seems much, much more relevant.
So you are not benchmarking "the OS" but rather the distribution, which includes whatever compiler version or flags they chose to use.
Honest question: If I take the exact same binary and shared libraries and run it on different distros, what am I actually measuring as differences? Kernel configs, filesystem, background processes? Does the distro even matter for that?