Why this item increases your health instead of giving you damage reduction? Wouldn't that be the same thing? Plus, this would get rid of extremely powerful interactions like Cho'Gath's ult and 
when combined with Stoneplate.
ForFoxSakes2 votesNot the same thing at all.
Heals would be much more effective if it gave + resists, while armor/MR shred and true damage would gain huge value
Weathered1 votesTrue damage would still be 100% effective despite the item's active.
GrandpaTheGreat1 votesYes, but currently Cho-Gath's let scales with HP, which means that Gargoyle's actually increases his ulti's damage
YumaS2Astral1 votesBut at same time, percentage damage would be less effective (unless it is percentage true damage, which is effective regardless of whether the item gives increased health or damage reduction).
If you are talking about Cho'Gath dealing true damage with his ult; he would deal less damage because he wouldn't get increased health (his ult scales with health) - he would still get damage reduction.