I think to help people make informed decision, it would be best to explain how the system work. Though it's not perfect when you have a lottery system, this is bound to happen. We had to make 1st and 2nd choice. Yes, some people din't get neither their first or second choice, but not because there were not enough space, but because they use a computer algorithm and run several matches until they find the match that get the most people their first choice AND the least people unmatched.
You also have a process in place where people that have special circumstances, can write an appeal letter to a committee with supporting documentation, that would explain why they should be given special consideration for a specific sites. In addition you can write another letter to whoever is the one in charge for the site you want, making a pitch for why you want them to pick you. I believe every site can choose up till 3 candidates
So show me a lottery system that let you pick only 2 choices and doesn't have people "unmatched". Considering the fact that rotation sites have a limited number of students they can take at the time, you need a system that makes sense, and I believe the way they run it makes sense.
At the end everyone gets a pick. Not everyone is happy but they try to make it in such a way that most people are happy.