To get a chance for a CR you need to be included in the top 100 while to have a chance to get a rare card you need to have ELO value higher than 1000. Playing ELO only gives you a chance to get cards, it won't give you cards every time.
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.
The Urban Rivals team is made by lovers of all kind of Collectibles Cards Games and Trading Cards Games like: Magic the Gathering, Dominion, Vampire, Yu-Gi-Oh!, Pokemon, Wakfu TCG, Assassin Creed Recollection, Shadow Era, Kard Kombat and Might & Magic Duel of Champions.