I have same feeling

You are right. It is really hard to write same thing with different words and expressions. The letters should be different as though they are from different writters. If the samples are close to your research field, it is ok, you just change a few, like filling in blanks. if far away from your research works, oh, man , you have to figure out how to dedate over your works so that the immigration offers think you are nice guy, America might be collapsed without you, earth could not turn around if not offer you greencard. Anyway, it is not easy. Encouragement with each other is indeed important for us to accomplish our tough writing task for NIW.