The only real RNG we have is all these bajillion procs and shit in 8.3. Which honestly is extreme RNG, but not really a class issue.
Mastery is not a problem after all the changes and Chaos Bolt auto-crit is awesome really. I shudder to remember things like Demonbolt in WoD where a lot your damage was riding on whether those two last DBs crit or not. Now that's RNG.