Can someone explain how come this gray item without any healing stats heals 12% better than a legendary?
The Flail has a much faster attack speed so you benefit more from Life on Hit if you have any on your gear. Thus getting 12.5% bonus healing.
To further extend my answer, healing affixes are :
- Life on Hit
- Life after kill
- Life per second
- Life per resource spent (only for melee classes)
The healing stat is the game's estimation of how much life you can regenerate over a period of 1 second depending on what healing affixes you are using on your gear. The exact calculation is unknown but it's safe to assume that Life on Hit is more efficient with a high attack rate.
It's important to note aswell, since patch patch 2.1.2 :
The "Healing" stat on the character sheet has been replaced with "Recovery". Recovery is an estimate of how much Toughness you are expected to be able to recover in combat and is calculated using a combination of your Healing, Life, and Toughness.The Healing number will still be viewable in the character sheet if you mouse over the Recovery stat
which is in my opinion more accurate.