Defiance gives you a buff that both increases max hp and increases healing received. Losing a buff is not the same as using a skill that costs hp. With that logic, you might as well not even use any defensive CDs because once you lose their buff, you take more damage. If you want to see skills that cost hp, go play some pvp in swtor where pug sorcs/sages will deplete their own hp so they can heal themselves back and at the end it looks like they actually did something (I haven't played in forever so idk if that's common anymore lol).
