Surprisingly, that flexible coupling is actually a good thing. If you look at helicopters, this is called a lead-lag hinge, and it allows the propeller to match flight loads when flying around. What happens is the blade advances in the hinge as it retreats in the airflow, and retreats in the hinge as it advances in the airflow.
(Watch a fully-actuated hinge on a helicopter: https://www.youtube.com/watch?v=Pu48f7s5Ru8)
This is because as the rotorcraft flies forward, the rotational velocity of the blades combines with the translational velocity of the aircraft to make for a different airspeed across the blades depending on where they are in their rotational arc.
Aerodynamically, this allows the blade to perform better in forward flight. In particular, as the blade goes faster to catch up it increases its airspeed and decreases the likelihood of a tip stall.
Structurally, the hinge removes all stresses about that axis[*]. In turn, reduced stress allows for a narrower blade root and a longer lived blade. In fact, it's very challenging to build a helicopter with a fixed root because the blades tend to fatigue themselves to death very quickly.
[*] By definition, a hinge is a mechanical device which provides for a rigid connection in all axes but the hinged one. A perfect hinge provides no resistance along the hinged axis.