I am still curious as to how 'aerodynamic' the fan blades are and how much they are just big paddles shuffling air backwards. The amount of ice 'acceptable' during walk around will always be a subjective assessment.
Of course as others have said the fan blades are aerodynamic and critical to propulsive thrust.
However the thread was mostly about ice on the blades and its detection and removal.
The aerodynamics is mostly about high power operation and the ice build up problem is about low power operation. At low power approach, taxi in and taxi out, those blades are not working like they would at high power and hence that is why the ice sticks.
For sure there is always the subjectivity of what your eye sees at walk-arounds, but this is addressed by your training and procedures. So in the end as long as you follow your training the ice issue is well managed