I got a chocobo to almost max stats for R60 (100 Maximum Speed, 92 Acceleration, 94 Endurance, 98 Stamina, 66 Cunning) and won almost every race, even against really good players (but most of them weren't good).

I used Choco Ease II, which restores Stamina when you get hit by a speed reduction. NPC do use these on you, but you can make sure you get hit by it by going into the purple on purpose, then restore Stamina.

-There's always one NPC in every racing rating that has basically perfect stats. You can hammer them with multiple debuffs, but they STILL stay ahead of you no matter what basically
I've noticed this one but I still beat them, so you just need to refine your technique.

-Many items are basically useless against NPCs who have abilites that prevent certain items from ever working on them. There are traits to be 100% IMMUNE TO CERTAIN DEBUFFS/STATUS AILMENTS.
I never noticed that because I'm always in first place and have nobody to use them on.