hahaha, honestly I noticed something is weird about max HP cards before but I didn't bother confirming my theory since most of them had negligible effects. I know some people who had been using some of those cards but didn't notice it either.
Today I tested it and I can confirm that every card that gives raw MAX HP bonus in the server gives 2x their stated bonus. That being said, fabre card gives 20k HP instead of 10k, arch angeling gives 60k HP instead of 30k, succubus card gives 200k HP and so Evil Tree card gives 300k HP.
Now I believe there's nothing wrong with the 2x bonus, it's just that most players aren't aware about it so they neglect it too. And some might still think it's useless. Regardless, I don't know if it will get nerfed or there will only be a correction on item description. The correction on description is preferable.
Aan suggested a 400k-500k bonus HP and I am sure he is not aware about the 2x bonus, but in my honest opinion the current effect of 300k HP bonus is good enough if you know where to use it and if you at least tried it.
The Decorated Evil Tree card is designed for low vit build, while most players seeks balance build, there are people who uses a more adjustable build and that build is only attainable using succubus card and Decorated Evil Tree Card.
This is a 1 base vit stat warlock and I got 1m HP using this build. You will only need 2 consumables if you want to reach 2m HP with same build and stat. Although unless you are rich I doubt you can use it as a daily build.
MAX HP Card works in some build better than tao gunka for these 2 reasons:
Tao Gunka is highly dependent on MAX HP which depends mostly on players vit. Evil Tree Card simply boost your max HP regardless of your vit. In short Evil tree is better for low vit build.
Tao Gunka boosted HP can no longer be boosted while Evil Tree card max HP can be boosted further by other HP% bonuses of cards , gears and consumables. It means with magnetite 15% you got 45k more HP from evil tree card, then another 20% from sleipnir so 60k HP etc etc. In fact without that armor my warlock HP only have 400k+ hp.. it boosted my HP by extra 600k+ because of other HP boosting stuffs I am wearing.