I disagree, it's already a powerful ability and it's one that's built into your melee attack unlike the Warlock's Flame Shield which is something you have to choose to equip and thus is a bonus to the added melee damage. Also, Disintegrate doesn't discharge itself if it's not enough added damage to get a melee kill so you can't waste the charge by not getting a kill with your attack. Unbreakable is a key ability for Force Barrier and I very rarely use the other options because it's such a powerful buff to the ability. However, if it was an ability that was rolled into Force Barrier or provided by an Exotic you'd be able to use it and War Machine at the same time which would be seriously overpowered.