Sure looks like blending to me.
They used to take some startling lumps out of the blades of the C130s at Lyneham and presumably everywhere else too.
I also agree with the comment about the vibration would have to increase a whole lot for anyone to notice.
I used to run old bangers when I was on Hercules and when leaving the carpark to drive home - it felt like a Rolls Royce.
That should give you some idea.
The missing paint etc IS erosion or particle blasting from the environment these poor s*ds operate in.