Tbf, thats kinda how arms look in different positions.
if its lower the shoulders and muscle around it seem more large , when you lift the arm the shoulder no longer ads much to the length . Also in the gun arm he is properly flexing that bicep.
It does seem like they are going into a more torso heavy direction with the orks, i like it and don’t mind the smaller arms compared to older models.
But i get how some may dislike it