I personally feel like anything that your chocobo gets after learning choco cure is just a bonus. It keeps me topped up while I'm on a DPS or a tank so I don't have to pause every couple of kills to let my health recover. It lets me concentrate on dealing damage when soloing as a healer. I don't need it to deal large amounts of damage, and I don't need it to hold aggro. If it is able to do either of those things, then that's nice, but it's also not a very big deal to me.
So, as far as I'm concerned, the chocobo levelling rate is fine. But then I say this as someone with only a rank 6 chocobo, on account of me just not seeing enough merit to focus on levelling it.
