Running a network stress test on an OS few people use isn't real world though.
That statement is so ignorant, I'm genuinely not sure where to begin (or, honestly, if it's worth the bother).
It doesn't matter which OS you run it on. As it happens,
flent
runs anywhere but Windows, including on macOS. Your router isn't running Windows. Your switch isn't running Windows. The core network at your ISP isn't running Windows. The Internet isn't running on Windows, either. When you flood your Internet connection with traffic and choke it because of bufferbloat (you lose packets because the buffers are full to overrunning and there's no fair queuing or other congestion control), it doesn't matter one jot whether that traffic emanated from a Windows machine, a Raspberry Pi running Debian, a FreeBSD server or a mobile phone. Traffic is traffic. Just the same, running an RRUL test (which is an industry standard, btw) emulates the type of traffic that will saturate a line in both directions and then measure what breaks. Did you even read the website?
What you said is akin to saying 'We can't measure the impact force of a 2 tonne car travelling at 70mph if that car is a Ferrari, because few people drive those. We need to test the impact force of a 2 tonne Ford car travelling at 70mph, because they're more common'... The marque of car is absolutely irrelevant to what's being measured, and why it's being measured. In that case, the salient variables are the mass and the speed, not what sicker is on the front of it.
In our case, the test is 'How does the connection's latency, jitter and bufferbloat present when under full TCP and/or UDP load?'. Where that test runs from is immaterial. Do you honestly think the Internet engineers at IETF, Cloudflare, RedHat, Google and others are all firing up Windows boxes because 'more people use them at home'? LOL TBF, I'm not singling you out here. Earlier, completely misinterpreted the difference between two sets of pings on an almost idle line (a speedtest is basically zero load). And that's fine. Not everyone knows too much about networks, or any other subject matter. The trick is to realise the things you don't know much about and (1) fix it and/or (2) not talk smack about it until you do.
If you prefer a test from Windows, give
this little fella a go and post up your results. It's the Waveform bufferbloat test and it does a nice job of properly saturating the connection with packets and then making pretty graphs of the results. It'll be interesting to see what you come up with.