Brawler was allowed to stack with brass knuckles back when the Luchador archetype came out. It was basically included so that someone could bring unarmed damage up to parity with a good melee weapon (+2 added to +1 = +3, along the lines of a one-handed sword), but only if they were willing to put a perk into it, which seemed reasonable.
Brawler + brass knucks isn't the problem. Death Claws and Dragon Claws both already starting out as +3 is the problem. Those things don't need any extra perks or other frills to bring them up to parity, because they get parity right out of the gate. Throwing Giant Strength or any of that other stuff onto them is just adding fuel to a fire that's already been lit. That's one issue.
Another issue, to me, is that I really don't think Dragon Claws (and maybe even Death Claws) should be using the unarmed combat skill anyway. Just because a big honkin' metal blade is stuck to someone's forearm instead of being held in their hand doesn't make it *not* a big honkin' metal blade. For example, I wouldn't consider the X-Men's Wolverine to be an "unarmed" combatant, with him basically going around swinging short swords/long daggers every which way to stab people.
To me, the questions are: Is someone punching/clawing something with a bare hand? Okay, it's unarmed combat. Are they a practiced "Brawler" who's really good at it? Okay, +2 damage. Are they wrapping those knuckles in metal or making those natural claws a little extra sharp somehow? Okay, maybe
that's worth an extra +1 damage, depending on circumstances. Or maybe even worth adding some additional special effect to it, like the AP 2. But making it a whole natural +3? No, that's gone well away from a "normal punch" into "this is something entirely different than taking a normal swing at someone with a fist". It's entered Wolverine's claws territory, something so *artificially* good that it merits being called a melee weapon, which is the use of something artificial that works in a different way than the natural body, and so requires different techniques to wield. Having extra-hard knuckles doesn't change someone's punching technique. Having claws that are a foot long, or able to cut through steel plate like butter, certainly would. They'd start swinging those things in different ways, to different effect. It becomes something that shouldn't merit the bells and whistles that were meant to help normal unarmed attacks keep up with melee. It doesn't need
That's my opinion, anyway. Personally I'd nerf Dragon Claws and Death Claws before I'd make any rulings that lead to unintended wonkiness. ("Yes, it IS strange how wrapping that metal around your knuckles makes you hit less hard. Reality's weird, champ. Don't think too hard about it.")