Youre kinda proving my point? You scaled it to headsize yes? Look at Torso lenghts, Limb Lengths, Etc. They are not the same, and no it's not just "a pose thing". The torso and limb differences generate different proportions which can ruin the design aesthetics. Check it out:
Both are what...Roughly 9 headlengths, though the concept is a touch shorter. Lets say that is pose differences. Fine.
Check now the Torso length comparisons. This is from the pit of the clavicle to the crotch. They end in different spots, with the in game being longer. That change has a knock on effect. Check where another Torso length ends - On the concept art, roughly at the knees but in game its midway down the shins. In concept art, tall elegant characters tend to actually follow the left a lot more closely, choosing to elongate the legs to give height. In reality, the in game model is a bit more accurate to real life - Torsos length roughly ends around mid to lower shin, depending how tall or stocky the character is.
What I suspect, honestly, is the elezen model is a modified model of the Hyur (which would make sense from a production stand point). Thats why the proportions arent the same between the concept and final. Most people I feel frankly would agree that aesthetically the concept designs proportions are nicer. They feel more balanced. The in game model feels off. Part of the reason perhaps the neck feels so long on elezen is that compared to the torso and head sizes, it feels off.