physical appearance

[Kallera]

Ehhhh...

Given the medieval setting, there shouldn't be too many overweight people. Without modern food production techniques, there simply should not be enough food for anyone but wealthy aristocrats to grow fat in any capacity.

Also limitation of modeling. But it mostly makes sense in-universe, diversity of body types notwithstanding.

Chocobos.

[Cilia]

Chocobos.

What about them? Are you perchance referring to the Fat Chobobo and Heavy Hatchling, suggesting their... girth (hee hee) is proof there is enough food for people to get fat?

Fat Chobobo's size is unexplained. He was apparently overfed, which should mean fewer greens for other chocobos (and by extension a number of sickly, unusable steeds), but since it's just a game there's no unfortunate consequences to this and Fat Chobobos are just funny. Plus greens, as vegetables, should be really low on calories anyway, so how he reached this size (beyond it simply being a differing body type from the garden variety chocobo) will forever be a mystery!

Heavy Hatchlings did not reach their great size by overeating greens (in fact their description says that chocobos cannot reach that size on greens alone), but by cannibalizing their siblings. Apparently. Sweet dreams!

... all jokes aside, we do know that Eorzea lacks the modern food production techniques we have. Otherwise the soldiers at Camp Cloudtop probably wouldn't be complaining about the lack of rations and attempting to grow their own food to compensate. It's not just that we can produce far greater quantities of food with modern techniques, but that we can do it with far less effort - farming without the fancy chemicals and machines people use nowadays is hard.