There is a flip side to fast.com, though: it’s much more likely that it will encounter throttled speeds on mobile devices, since many unlimited plans keep the connection to Netflix artificially slow.
Not endorsing that for a second but I was using fast.com as an absolute measure of internet speed until I realised this. But speedtest has the issues you’ve outlined too, there are very few 100% reliable options!
The flip side was and I guess still is the exact reason for existence of fast.com. ISPs were throttling Netflix, so Netflix rolled out its own speed-testing service on its own infrastructure to publicly shame ISPs about the throttling.
Without knowing about that background information, I suppose use of fast.com is a bit tricky.
