The Raen have been stated to have heavy association with Doma (See naming traditions), but most Domans don't look like Elezen-esque men and Midlander-esque women.
It's not very possible to have that sort of split, and it definitely doesn't occur in nomadic societies. If your society is going to need warriors, there's no good reason to cut off (And this assumes that Au Ra follow 1:1 sex ratios like every race besides Miqo'te) half of the population when it would build weakness. The second an Xaela tribe goes "Hm.. why not make it so our men are a bit faster in builds so they can outspeed the other men" or "Why not focus our women on more strength builds so that they can overpower other tribes' women?" they might have a pretty solid advantage. It's why such sexually dimorphic builds within the same race of humanoid creatures doesn't happen, especially not in a nomadic culture, intelligence and strategy doesn't allow it.
This hypothetical fight seems fun, so I want to explain further in it, as I feel you all are really overestimating speed and underestimating strength! The lalafell has to divert it's attention to two seperate fronts, dodging and still attempting to attack, all the Roegadyn has to do is defend itself and occasionally swipe in the direction of the Lalafell to keep them moving. Moving the entire body to dodge attacks takes a lot of energy, no matter how small and light they are, moving their entire bodies will take so much energy. Eventually our Lalafell rogue will exhaust themselves and become sluggish and that's when the Roegadyn simply takes a quick cleave and the fight will be over. Unless our Lalafell rogue is built to be the point where they could push back a full sized Roegadyn, they're not going to win, and a Lalafell with that sort of body shape isn't going to be lithe or even have that much of an endurance shaped build!