I can see how frustrating that can seem, but don't see it as a negative thing. By reposting your post, he exposed you to more people than would normally see your own post, especially if someone has more followers. So in a way, he did make you a favour because maybe as a result of mentioning you, some people have followed you because they liked your content. I don't think steemit is unfair in that sense because a person's reputation and steem power allows them to have more exposure and thus more upvotes which brings more money. I once posted something and made few cents, about an hour later, another user posted exactly the same thing but in his words, and he made a LOT of money. So I could've been mad about it, but at the end of the day, you shared your content to benefit others, and while our efforts are not always rewarded, we achieved what we set out to do, which is help others or inform them of something. I hope this makes sense.