angular momentum, spin velocities, and everything else all add up to the amount of force being applied to an object. when an object hits another the total force applied is equal to all the forces (no matter the source) being applied in that direction as well as the components of forces being applied in that
general direction (ie if you were to draw a line down a spinning blade and it was hitting another to the left of it. all forces in a direction on the same side of the line as the blade being hit would have a component force that acts in the same direction as where the point of contact is). as well as when both blades hit the forces of the receiving blade are applied to the attacking blade, and with all the action-reaction forces there is also reduction resulting in possibly a lower net force acting on the blade.
as well these blades do not weigh too much. all of these parts are measured in grams where as force is described as kg/m*s^2. so the actual forces are quite small. when you take into account how thick the plastic is, as well as the designs and supports intended to reduce stress and prevent compression/expansion of the plastic, as well as the thickness of the plastic it is still unlikely that they will break from simultaneous collisions. and even if the AR hits a WD the ones that stick out the most are the Wide which are extremely light which reduces any kinds of force created through collisions
edit
o and plastics can be VERY strong. plastics are used because they are cheap to produce yet are still able to do a job that metal could be used for. they are designed to be strong and can be just as strong as the thin metal used in the WD's
Engineers: If it wasn't for us there'd be no mechs for emo pilots to fly