What sort of evidence do I need to provide for you to be satisfied?
Sacrosanct Martyr trades your HP for damage. You can trade up to 5 hp for 5 damage. Except that as a power, you are doing it at the expense of other powers, say Exorcism or Absolution. for now, lets assume that you are only using one power/turn, which is normal.
Lets say you do 5 damage, the maximum. What was your trade like? Well, its easy to say you traded 5 hp for 5 damage. Except you didn't. You lost 5 hp for 3 damage. Or, if you had Absolution out, you lost 5 hp for 2 damage. This is because you may only use one power per turn, you can't compare against a null void, you should be comparing against Exorcism or Absolution, compare Sacrosanct Martyr against what else you could do on your power phase. Since you could deal 3 damage anyway with no HP loss with Absolution, you have just spent 5 hp to deal 2 extra points of damage.
Suppose damage is boosted, say +1. With Exorcism or Absolution you deal 4 damage. With Sacrosanct martyr you can lose 6 hp to deal 7 damage. You've now lost 6 hp for 3 extra damage. It does not scale better this direction. At +2 damage, Exorcism does 6 damage, you could use Sacrosanct Martyr to lose 7 hp and deal 9 damage, trading 7 hp for an extra 3 damage.
If damage is reduced to enemies, but not to yourself, Sacrosanct Martyr can do 5 damage to self to deal 4 damage to enemies. This is where it starts to look a little better on account of Exorcism being only able to deal 0 damage. Absolution could deal 2 damage though. You lost 5 life to deal 2 extra damage. If your damage is -2, you could deal yourself 5 damage to deal 3 damage, Absolution would only deal 1 damage, and as you can see again, you lost 5 hp to deal 2 extra damage. Now sure, maybe you really want to kill a Gene-bound guard or something, I did say in the guide that I might play this and use its power as a desperation attack if something really needed to die and there was no other way to do it.
Suppose you also have Embolden out, Now you can use 2 powers/turn. And Embolden deals Radiant damage right? Bonus! Except... not right. Embolden deals its radiant damage at the end of your turn, which means that it can't combo with Sacrosanct Martyr. Too bad!
Now it's easy to conclude what I'd probably say here: why aren't you using Exorcism/Absolution instead of Exorcism/Martyr? Well, maybe you don't have Absolution. Lets assume that because otherwise using Exorcism/Absolution is exactly what you should do, as you can plainly deduce from what I've laid out above. Now all your damage doesnt have to compare against Exorcism, so ... thats good for Martyr. On the other hand, you're taking more damage because of Embolden, so it had best be worth it.
At +0 damage you lose 7 hp to deal 5 extra damage., +1 you lose 9 hp to deal 6 extra damage, +2 you lose 11 hp to deal 7 extra damage. You can't sustain this for long.
If there is some sort of a global damage negative, we don't have to cover this with Embolden out becuase remember that Exorcism is useless, so you may as well cancel Embolden, and see what I wrote about just using SS Martyr alone without Embolden. Hint: You're spending 5 life for +2 damage over Absolution. But I did say we weren't talking about Absolution in this section, didn't I? So you lose 5 hp and deal 4 damage with your power phase.
So when is the best time to use SS martyr? Well its the last one. When your Exorcism is reduced to dealing 0 damage and you don't have Absolution. This works out to be the highest ratio of damage dealt/hp loss when considering what else you could do with your power phase. That ratio is 4:5, or 4 damage dealt per 5 hp lost. Remember if you have Abolution it's better to use that instead.
Every other time your ratios go down dramatically. To reiterate, at +0 damage it is 3:5, or 3 extra damage per 5 hp lost if you do not have absolution. If you do have Absolution, it's 2:5 instead. At +1 damage dealt your ratio is 3:6. 3 extra damage dealt for every 6 hp spent.
Simply put, this simply isn't a good trade for you. So if you use SSmartyr at +0 (and you do NOT have Absolution) and do this 4 times, you lost 20 of your 30 HP, you dealt 12 more damage than you otherwise would have, but you've likely nearly killed yourself to do it, (likely you're less than 5 hp right now, if you're not already dead, as the enemies will be hitting you too.). So yes, I'm quite confident in saying using SS Martyr as a primary form of attack is suboptimal.
