The FRATs I've used have all been kind of garbage except for one company I worked at to be honest... Every place I worked had some scoring system except for one and there was no actual reason for the scores under the hood, it was kind of funny...
The place that did it right broke the FRAT down by each phase of flight down and looked at the risks in each segment. It was really cool, because let's say the weather sucked at the departure airport, but everything around the departure was fine, why should that drag down the rest of the flight? If it was borderline, you'd note it in the FRAT, call the CP or DO or their designee, "hey man, the weather sucks here, and if I leave I won't be able to get back in, but if something happens there's like 6 airports within 20 minutes, and the weather is good for the rest of the flight?" They'd ask a few questions, then either choose to accept your strategy or not. You didn't end up with really bizarre situations where the flight was moderately sketchy the whole time because you were borderline the whole way (if you needed too many mitigations, it was an automatic scrub), and then also like if you were having a bad day for something, there was a mechanism to put a guy on easier trips. "Bob has flown 40 hours this week, it's been bananas, he's fatigued - ok, he can't accept any mitigation then."
I liked this a lot better than a points system where the numbers were clearly made up by how scary whoever made the FRAT thought that particular thing was but you could end up with a crazy situation where you'd be mashing ice on the whole flight, land at mins at both airports, have to hand deice from some shack, are flying in your region of circadian low, and are 2 points away from scrubbing but there's a thunderstorm 40 miles away from you, moving away from you on a clear VFR day and you have to add +6 or whatever because the "convective weather within 100NM? - +6" or whatever.
As far as I can tell though, literally none of the FRATs I have ever used (and in my career I used maybe 10 different methods for mitigating risk?) had any basis in any statistics.