And there's still a random factor involved.
So let's say if you're not in the Top 100, but still have a really high ELO score, e.g. 1200+, it doesn't guarantee that you'll have a rare card. Everyone has equal chances, as long as your score is 1000+. But it's a whole lot better to be in the top 100 because, first you have a chance of getting a Cr, and you win at least 5 credits at the end of the week.