I don't think it has a niche or role anymore. Some years ago they claimed to be fast. [0,1,2]
I don't know where did you get that FreeBSD is regarded as the fast one. I think it is considered the popular/general purposed one, without a single aim like openBSD or netBSD have.
You are right, it seems much faster than freeBSD in a lot of areas and relevant benchmarks (real world programs and scenarios).
They got similar overall results, but as far as I see, freeBSD is mainly faster in irrelevant benchmarks. (This is an opinion based on a glance of the phoronix article. I haven't spent much time looking at the results, also I am not an expert at benchmarking.)
I mean it's just impressive for such a small project, and benchmark's...well they just count for your very own workload..it's good to find regressions but not much else.
It is fast, maybe the fastest of all BSD's:
https://www.phoronix.com/review/bsd-linux-eo2021/2