[PSA] Soraka rework scaling explanation!

Since Riot started teasing Soraka's new kit (thanks, Vesh!), I've been seeing a lot of speculation and discussion about what proper itemization is on her. Without knowing her full kit, it's pointless to get too far into specifics, but there's still a number of misconceptions I'd like to address.

What we know is that she's going to be an infuse healer, meaning that she burns away her own health to restore health to allies. Specifically, her heal will cost % max health to restore an amount independent of the amount of health she spent on it, and presumably with a small to moderate AP ratio. There's a few things I'd like to explain. Note that I'm ignoring health regen, negative resists, and penetration. They're all largely irrelevant to the broader points.

• Healing is strong: The dual of healing is not regular damage, but true damage. If you have even just 100 armor, and get healed for 200 HP, it will take 400 physical damage to burn through that heal. That's why the numbers on heals often feel kinda low. The more resists your target has, the better a flat heal will be.
• Effective HP is all that matters: What determines how tough you are to kill is your effective hit point (EHP), which differ depending on the type of damage you're facing. If you're facing only physical damage, you'll take HP(1+armor/100)* points of pre-resist damage to kill. If you're facing magic damage, change that armor to MR. Against true damage, there's no defense, so your EHP is just your HP. Setting aside gold efficiency, you'd generally rather have HP than resists, because HP is good against all three classes of damage.
• % Max health removes HP from the equation: If you're facing % max health physical or magical damage, the amount you can take is proportional only to the relevant resist. Building HP is not counterproductive, but it is gold wasted. To give an example, if you have 1000 health and 100 armor, you have 2000 EHP vs. physical. If you suffer an effect that deals 20% max health physical damage, you will drop to 900 health and 1800 EHP, a 10% drop. If you instead had 2000 health, you'd start at 4000 EHP and drop to 1800 health and 3600 EHP — again a 10% drop. If you were at 1000 health and 300 armor, you'd start at 4000 EHP and drop to only 3800 EHP; only a 5% drop. In this case, resists are more effective. Also note that with more health, the % max health somewhat reduces the effectiveness of that health against attacks that are not % based.
• True % max health is agnostic: There's two places this applies. % Max health true damage, and % max health healing. In each case, it doesn't matter how much defenses you've built, or the balance of those defenses between health and resists. If you suffer a 10% max health true damage effect, it will take exactly ten of those to kill you, no matter what you have. Similarly, max health to health healing increases your EHP by a fixed proportion of the maximum. In other words, if you're playing Maokai and the other team is all physical, feel free to just stack armor: your passive will heal you fewer HP than in a build with health items, but each of those HP count for more.
• Soraka's new heal is agnostic: Suppose Soraka's new heal costs her 10% of her max HP to use. She can use it exactly ten times before keeling over. Building health and resists will not help her weather the price of healing. In fact, if we assume she'll use it several times, durability items of any variety will be less gold efficient on her. If she burns away half her EHP out of martyrdom, that's half the gold value of her durability items gone.

I don't know what Soraka's Q will be. It's something that makes it safer for heal to more, but I don't know what form that safety will take. If it's like Vlad Q, we come to one conclusion, but if it reduces by a percentage the damage dealt to her by the enemies it strikes, we come to a different one. So let's ignore the unknown tools Riot gave her to increase her safety.

Durability itemization on Soraka will be less gold efficient than on any other champion. That's not to say it's useless — you'd still like to make sure that you don't get assassinated before you even get to use that heal — but it does suggest that she's probably better off building glass cannon syringe than any more balanced or defensive build. So supporty defensive items like the Relic Shield line, Aegis of the Legion, or even Mikael's Crucible are less gold efficient on her than on any other champion. Unless her AP ratios are astoundingly low (and see my first bullet that even low numbers on heals are deceptively powerful), she'll probably be better off going for mana, mp5, HP/5, CDR, and raw AP. In other words, classical support stats.

How's this analysis seem? Is there anything I'm missing? Anything else you'd like explained? Thanks for reading!

EDIT: Vesh has strongly hinted that her Q will provide a flat heal. In this case, though health is still pretty bad, resists get a fair bit better. I'd have to see exact numbers to come to any conclusions on their absolute efficiency, but this certainly makes Crucible and certain armor items a fair bit more appealing.