Chocobos were used in battle in the FFT series. I don't really see it as a problem. Seems like you can have one out per large group, but I also heard mentioned in an earlier interview that people that are duo'ing are allowed to both use theirs.

I don't know if the strengths of the chocobo will scale better than the adventuring partner from FF11 or not. If I'm raising my chocobo to be a tank and it has the strength equivalent to a level 50, it damn well should be able to tank according to what a level 50 damage dealer can do fighting at a normal pace.