I think it's a little strong to say that XLR is better in every way. The only important benefit XLR offers is improved noise rejection, but at the cost of greater complexity, cost and size. Noise rejection is of greatest value with very low signal levels, such as microphone cables, long low-level cable runs, and in electrically noisy environments. All tree are common in pro audio, which is likely why it's favored in that environment.
However, if your RCA runs aren't contributing noise to your system, XLR is not better in any way.