User blog comment:Willbachbakal/(Item Concept) Revamping Life Steal/@comment-5588011-20150826183220/@comment-1330314-20150901160752

and have many advantages that are locked out to marksmen and can be emphasized, such as their tankiness and inbuilt sustain. Reducing the life steal of others is not part of their identity. They're weak to BotRK, but already have the tools to deal with marksmen pretty well (Nasus's W is one of the most devastating debuffs to be used on a marksman, and it's point and click, whereas Mundo's sustain can outpace the DPS of marksmen, and he has both a long-duration movespeed steroid with a near-permaslow).

The idea with making life steal unique is that it would enable far more diversity with the effect and its use, as opposed to keeping it as the single effect it is now. Late-game life steal should be unique, tailored to a specific playstyle and powerful enough on its own to never warrant stacking. Put another way, it would make no sense to make life steal non-unique.

The fact that life steal works with fewer stats does not mean it scales too hard early. If anything, the above life steal is a lot weaker early game, as it's about the same against champions but far weaker on minions, so rushing the item would incur heavy costs early on without too much of an immediate payoff. The sustain is also tuned around the life steal attained by marksmen, and so would be a buff to AD damage-dealers who don't rely as much on crit. Sustain has been implemented in a similar way on on live, and it hasn't produced any of the catastrophic consequences you're listing here, so I don't think changing life steal in the above way would create those issues.