When you hear hoofbeats think horses, not zebras. No online freelance opportunity brokering board does the job well; Upwork is merely the least bad. Freelancers have little ability to control what you see.
I am alerted from time to time that I failed to meet all of the client's requirements, and see that "English: Native or Bilingual" is highlighted. That is because I have not taken a test to document that I speak, read, write and understand English. If the client is unable to discern from my response that my English is up to the task, I don't wish to work with that client.
As for JSS, there's a prize for anyone who can say with certainty exactly what is measured and how. I ignore JSS because its components are kept secret. I ignore all feedback with no narrative, regardless of number of stars. I have had remarkable success with hiring freelancers with no track record but with whom I explored a fit. My own JSS went down the drain at one point when I was in the midst of becoming ill without recognizing it, and failed to deliver, followed shortly by a job in which the client gave me a poor rating because I wouldn't work for stock in his company. I don't care. You probably shouldn't either.
In commodity services I suppose the algorithms make sense. In non-commodity services, it's a crap shoot.