Destabilizing rounds is only useful for void titans running controlled demolition for extra healing. As void titans are the only ones who get any benefit out of volatile besides damage. At which point why not just run a damage perk that doesn't need kills. Even then if you're on void it's just better to use the fragment that gives volatile rounds on grenade kills. It is also pointless to remove the cooldown as the perk is capped by how fast you can kill enemies and there are no fragments that give you a benefit for using volatile. Hence why void titans are the only class to benefit from it. Incandescent and volt shot both have fragments that build into getting ability energy back while volatile can't. As for repulsor brace it too is also a pretty worthless perk (since void overshields only benefit titans in regards to gameplay), but you don't have to sacrifice a damage perk for it and hunters and warlocks can both inflict suppression and weaken which are better for triggering the overshield.