There are basically two enchants that offer any kind of EHP: mongoose and blood draining.
Mongoose is equivalent of 21 stam worth of EHP when it is up (240/11 = 21.8 or something like that). Basically it is 210 hit points.
Blood draining is an up to 2k heal. The efficiency of blood draining would have to drop to ~14% for it to be worse than mongoose in terms of EHP if you assume mongose has a 100% uptime, which it DOES NOT, especially for warriors.
If you never need blood draining on a fight, then you don't need mongoose, but saying "eh I don't need the EHP, so I might as well go for dodge or threat" is akin (imo) in my mind to saying, "eh, I don't NEED 40 stam on my bracers, that enchant individually won't save me, I might as well gem 12 defense or attack power or strenght or something."
I can pretty much guarantee that anyone that says that would get laughed out of the forums. It's not individual enchants that allow you to have enough EHP to survive something, it's about the sum of all the little benefits that help you.
Blood draining is a smart heal when you need it, though I would gladly take 200 stam worth of REAL ehp any day than 200 stam worth of effective healing, but that's not the enchants blizzard gave us. The only enchant that provides anything close to what might be considered "reliable" EHP (not necessarily life saving EHP, just EHP) is blood draining.
I'm putting my foot down.
See, it's down... mainly because I'm currently sitting...
Oh and blood draining works for all forms of damage, mongoose and bladeward only work for physical damage.
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