1. All things being equal, R1 does give you an edge over R2 in terms of the probability.
2. If you get dinged in R1 then you have an option to apply in R2 so it becomes your plan B.
3. You hedge your risks by applying to as many schools as possible by applying to both R1 and R2.
So, in short – if you have taken the GMAT then it is better to have a strategy to apply in both the rounds.