You haven't shown evidence of any "protrusion" or marking, I've noted. The area of "buffing" might be a little higher (1/1000th of a mm) but the darkness is caused by someone repeadedly forcing the post back and forth while the clamp is tightenened. That caused the inside of the frame to "darken".

Go ahead, buy a new post, and if you swivel it back and forth, expect the same marking. I can't help you there. I can tell you that to ream a seattube to remove obvious signs of misuse, is not going to solve your problem.