What if: New stat called sustain affinity

Sustain affinity would be a modifier for all champions, a stat that would be rather hard to change. This would be used to balnce sustain around champions. Like ranged ADC's with higher range would have lower base sustain affinity, and champions like Aatrox who need to drain tank would have higher sustain affinity.

What sustain affinity would do is modify the amount of lifesteal/spell vamp/vamp. This would allow for variable gains from combat sustain, without making blanket changes for champions.

Sustain affinity could then perhaps be modified slightly through one or two items, some masteries, and/or some runes.

As such, we could have champions have to itemize for HOW WELL they benefit off of combat sustain. Not just itemize for combat sustain, but for how well they benefit off of it. What this means is that we could have champions who benefit like crazy, and then those that need to invest a lot to have just as much combat sustain as others. Spell vamp broken on Vlad? Make him have lower base sustain affinity, thus making him want to prioritze items other than spell vamp.

Overall: how does a stat called sustain affinity that modifies combat sustain sound? By adding this, we could bring back spell vamp, and balance lifesteal once and for all.