The only thing I would point out is rat king is an exotic while you can choose another exotic to pair with luna. With that said, I have luna, but I don't use it at all because I have several better options...like my rangefinder service revolver innagural address (which I used to CONSISTENTLY outplay luna users)...there are absolutely guns that can compete but people get frustrated by one quick death to a Luna. Tons of people are using it so it seems like they are constantly dying to it. It's definitely not overpowered and I would say it's not even the best crucible pinnacle weapon, neither is NF. Recluse is such a better option and it covers close range too so you can pair it with a pulse or long range hand cannon like Ace. People blow the strength of Luna WAY out of proportion imo