I'm not sure if any scale would make sense, though. The true thing to be fined for should be "driving unsafely", of course, whether that means driving too fast, braking suddenly, swerving, changing lanes without warning, etc. The thing is, the unsafety of all those things depends in very large part on the cars around you and sometimes on the road. (Driving at 100mph on a straight, flat freeway with no cars nearby is safer than weaving between a bunch of 65-70mph cars to maintain a speed of 80mph.)
But it would be really hard to come up with an objective algorithm to calculate how unsafe a rule violation is, and even harder to implement it without a vast array of cameras. So ... they implement an enforceable set of rules even if it's not a good one. (On a related note, it bothers me that driving with more than some arbitrary blood alcohol level is illegal, but driving after e.g. staying awake all night is not, even though the latter is worse[1]. Likely this is partly because checking BAC can be done fairly directly with cheap equipment, while checking how recently someone slept is... I dunno, there might be ways to mostly do that with good equipment, but I assume it's currently impractical.)
[1] "Being awake for at least 24 hours is equal to having a blood alcohol content of 0.10%. This is higher than the legal limit (0.08% BAC) in all states." https://www.cdc.gov/sleep/about_sleep/drowsy_driving.html