Oh, belatedly, for the more anal about anatomy. Spoilered for those who hate science in fantasy.
The biggest problem with the XIV Chocobo design is their legs. They drive me crazy.
The general rule in all birds is that the farther the legs are back on their body the worse they are at walking and running. As a runner, the Chocobo's legs should really, really be towards the middle of their body. Birds with legs that far back would be terrible at escaping predation on land.
Now, Galliformes can get away with legs relatively far back on their body because they're usually very strong burst fliers. They can get into the air quickly due to their short, strong wings. Galliformes aren't going to be running to escape a predator.
Since someone mentioned an Ostrich, look at how centered their legs are in comparison to their body and compare that to the XIV Chocobo design up there. And going off my Anseriform example above, compare the leg placement of a Snow Goose and a Western Grebe (Grebes are a pretty extreme example, though, and also not an anseriform). Snow Geese spend a lot of time foraging and nesting on Land, and Grebes are basically water-only divers.