I don't really use my chocobo outside of leveling stuff, he's rank 7 and I've been playing since ARR. I think they level stupidly slow for their purpose, as most people aren't constantly using them outside of leveling and fate farming. Now mind you I don't really care about my chocobo's level or I'd use the stables more, but I think they deserve a exp buff from combat, as rank 7 over ARR and two expansions of leveling through MSQ is kind of pathetic.