giving lifesteal/spellvamp ability to ignore 20 or 25% of target resistances
I think something like 20 to 25% would be modest. Or maybe have it as a mastery point either in offensive or defensive masteries. Would help cope with tanks. The problem with the old lifesteal was that it was op vs mages who couldn't sustain but it did allow for ADCs to survive thing like thornmail. By lowering the overall cap on lifesteal item/quints it let tanks do as they please. If you can't beat them join em. If you can't out damage their tankness early game perhaps being able to better sustain their damage would help.




Of the 4 essential marksmen stats: lifesteal, as ,ad and crit. the last 3 are pretty accessible. while lifesteal is the least accessible. The ratio is disproportionately slanted towards late game/on route to completing a 3500 gold item.
(comparing the cost of tank items to BT. Its a lot easier to stack defenses vs adc than it is for adc to reach BT while being expect to deal damage).