If you're going to be in a warrior culture, you're going to want to be as fit as possible, which generally requires being bigger and brawnier, you'll either be fighting/training, hunting/gathering, or doing a plethora of activities within the current settlement they set up, all of which would require physical strength. The bit of lore we've got for the Raen seems to indicate they've been with the Domans for some while, yet neither the Domans or Raen are that indicative of being too physically orientated. Besides, that's irrelevant, as no one seems to be arguing for the Raen women to be buff and stronger. Having the Xaela eat relatively poorly would be a horrid idea considering they're also warring with each other, lack of nutrients means a less healthy body, a less healthy body on the battle field means you'll be the one losing your life. Plus, saying "Carrying capacity is limited therefore no food" is silly, for example in Native American cultures Tipis weighed over 400 pounds from their poles alone. If the Xaela can manage to carry their temporary homes, then they probably could carry their food supplies too.
No society works like that though (Though you could be joking in which case, sorry! >.> ) If the lore in this game is to make any sense or be immersive, it ought to make sense. Societies can't just exist on silly rules like that.
Petite-girly girls can be "hellraiser wrecking balls" but that's not my point, my point is, in a society in which has the definition of "Warring tribal nomads" petite girly-girls would be in the minority. While Final Fantasy might have good examples of "petite girly-girls" kicking ass, it doesn't make sense for an entire society to be filled with them. Strength and presence in battle is probably emphasized, as this is a culture that's "Warring". Do you honestly think someone petite and small will be more threatening than someone with more size and muscle? Compare Lalafell to Roegadyn, which would you prefer fight in the field?