What if Lethality became less effective the longer a fight goes on?

So it starts at full strength on the first physical damage done and every second it becomes 25% less effective multiplicity.

Stacks up to 5 times and is applied everyone who has Lethality meaning a Jhin who bought Ghostblade starts attacking 3 seconds after Riven who has Edge of Night does not get the full power of the Lethality and in turn is only getting 42.18% effectiveness from any Lethality he has and will be reduced even farther as the fight goes on.

refreshes after 5 seconds.

In other words a champ having 40 Lethality at the start of a fight/trade will be reduced to 30 after one second then 22.5 followed by 16.875 etc.

Number could be adjusted but this is jsut an idea to make the stat have more clearly defined drawbacks.

Last I checked Lethality is suppose to be an assassin quick kill stat and not a prolonged fight stat. This suggestion makes it more of SURPRISE stat that you might expect form a sneaky assassin. Yes this would mean it would be good for poking and all inning a target who you kill in 2 or 3 seconds but far from ideal against the enemy who has 200 armor and 4000 health and takes 5+ seconds to kill. This would make items like LdR and Black cleaver far more idea in place of Lethality against tanks basically all practical situations.