Extra healing from lifesteal or similar effects should be situational or locked behind a condition

Just to explain, here is an example:

Someone who deals 200 damage with 30% lifesteal on a minion/champion with more than 200 health left (like, lets say about 400) will theorically heal for 60 Hp

Someone who deals 200 damage with 30% lifesteal on a minion/champion with LESS than 200 health left (for example, only 10 hp) will STILL heal for the same amount, while theorically it should be 30% of the damage dealt (in this case, only 3hp)

This shouldn't be a thing, or at least it should be limited. This strongly gives an advantage to champions with built-in damage/sustain in their kit or those who uses runes for it in the laning phase, since they can outlast the opponent simply by last hitting and healing from damage that they didn't even do.

My opinion/idea/proposition would be to remove entirely this aspect from the base kit of every champion and give most final sustain/survivability items a passive who brings back this effect. Example: an ADC with FleetFootwork/healing runes, or even a champion with built-in sustain like farming early wouldn't have access to as much healing from last hitting minions, but let's say we add the effect "Oversustain" (Calculates healing effects like lifesteal with calculated damage instead of dealt damage) to items like , it could potentially help getting rid of a frustrating mechanic early while still giving the opportunity to sustain-based builds to heal for incredible amounts in late game. Since this would gut some several healing options in early game, this could also bring the opportunity to actually buff some sustain sources who dosen't work like they should like 's passive since, by buffing it while adding this new gameplay depth, it could give him the opportunity to be realigned to the late game where he is supposed to be and less early-midgame while keeping him under control.

This is quite a dumb suggestion and would need some severe tweaks, but I really do think we could bring back the game into a more stable state with longer games, since slowing potential fights in several places on the map early would make scaling longer. Top lane won't trade as often since sustain would be more scarce, slowing potential pushing. Jungle won't gank as often/as soon as before since cleaning camps early will leave them with less health (this could also replace the placebo that was the scuttle upgrade, so we could revert those changes that a vast majority of junglers didn't want and they won't be as intidimating early as pre-scuttle rework, just like how its supposed to be). Midlane will probably stay pokelane. Botlane will have more impactful and thought fights, since they won't be able to farm and recover as fast as before.

Just my little thoughts on this. What do you guys think?