Saying that we're (we, being Vengeance mains) "balanced around" implies that the entire spec revolves around FbP, it's just not that impactful. Could it have some influence? Possibly. The entire spec being tuned around 1 RPPM from a single RNG trait? Doubtful. What you described is exactly how it already works, since it already functions as a bonus. You could literally never get a FbP proc and be fine. Play the spec like it doesn't exist and be fine. While I don't put a lot of stock into Blizzards balancing team lately, I would give them enough credit to believe that they aren't stupid enough to be basing the entire spec around a single trait with an RNG proc of 1 RPPM.