Welcome, IIF. Sorry you have to be here.
I have moved this thread to "Newly Diagnosed," so don't worry about where to post things -- we will put them where they should be if needed.
There is no formal definition of slow vs. rapid progression, though you can see others' FRS curves on PatientsLikeMe if you care to. The FRS scale is a very rough snapshot of function and only measures a few things, so we don't take it too seriously, though a certain score is required for some clinical trials.
However, based on published data over time and experiences here it is fair to say that living less than two years after diagnosis vs. living more than four or five are the ends of the spectrum and that most people fall in between. You will see that a "median" [half more, half less] life expectancy is 2.5 years, but those numbers are kind of old.
So here, rather than worry about trend lines, most of us prefer to focus on what will gain your PALS the best balance between quantity and quality of life.
Those things include, but are not limited to: avoiding falls with appropriate mobility devices, respiratory support [BiPAP] as soon as it's needed, maintaining weight with a balanced but not obsessive diet, hydration without bathroom visit concerns, physical activity that's not exhausting, active-to-passive range of motion exercise, a bed setup that allows for deep, refreshing sleep, some kind of hobby or activity that's enjoyable, interaction with nature, pets, family and friends.
Best,
Laurie