This was pretty much explained in this guy's blog http://na.finalfantasyxiv.com/lodest.../blog/2077797/

But yes I do agree that Rating system should be adjusted to your current stats and not solely on Max Stats + Rank + Pedigree. Mine's a 15/20 Chocobo so the max rating I can get is 276.

Looks like I'll have to use it to farm and retire (TT is too boring for me). I'm just curious if a properly fed 15/20 can stand a chance in R300 races.