I'm going to disagree with this. The insta kill can only be used at the most 2 times per game (I'm a warlock) so unless you have a bunch of idiots sitting in one spot you are not going to get much out of this. Also COD has this with choppers and jets and all kinds of mines and stuff. I own higher levels in this game but at the same time, I get owned by lower levels. It has ALOT to do with skill and not just "perks" you are talking about. Sure some weapons are not fully balanced but it's no where near as broken as you are talking about. The shot guns are the only thing that's over powered but they can only be used at close quarters. So you can't just run into the enemy like an idiot. The same thing goes for insta kills abilities. At the very most the abilities act as an "o shit button" at times to get one last kill before you die. I'm sorry but it just sounds to me that you are pissed because you got rekt too many times.
The break comes in that the Golden Bullet can be used far, far more than two times per game as you get multiple shots, is not range limited like Warlock or Titan, and, in general, I have found that it actually returns at least four to five times in a slayer match when I am playing well and getting a constant stream of kills. The gun is just stupidly overpowered, can completely flip the flow of a group fight as you whip it out and murder a whole group in short order, and then more kills feed your gauge. Rinse and repeat.
Levels are irrelevant as a metric (to the point where it seems you don't understand how the game works), its the gear that matters as the level based stats and damage are standardized but the gear advantages to stats and (reload/cooldown) speeds are not. You could be fighting a complete idiot level 20 with trash gear, or you could be fighting a grinder with min-maxed gear. The differences can be staggering but they aren't tied directly or obviously to the levels.
And don't give me the "rekt" nonsense. That's not how discussions work. These abilities are no more an "o shit" button than playing in Halo and suddenly having a rocket launcher appear in your equip slot with full ammo.