Started to question the life steal/spell vamp mechanics

Whatever happened to spell vamp? for mages like brand whats really out there i mean u got ravenous hunter which does"Heal for 2.5% (+ 2.5% per Bounty Hunter stack) of the damage dealt by your abilities, on-hit effects and items. Benefits from Heal Power." revitalize which does "Incoming healing, incoming shielding, self healing and self shielding are increased by 10% while you are below 40% health." physical attack champions have tons and tons of life steal items they can use but life steal doesnt help burst mages like brand how can we help support our mages health sustain to that of an adc with even just doran's blade life steal at of level 1 i mean doran's ring yes gives mana regen and also on minion kills mana restore but how can we mages sustain health mid-late game? idk i just think its stupid cause armor doesnt do nothing to protect u from auto attacks mr is busted cause a mage can only do burst dmg and mr can negate some of that. so how can we mages stay in fights long enough to survive if all of our abilites are on cd and cant even regain health without red buff late game