There are too many lethality sources
There's a reason that the only magic pen items in the game are 
and 
. Even Liandry's is niche instead of being designed as a "bread and butter" item. On top of that, mages are typically more dependent on mana, so instead of just rushing pen they have to buy mana items.
At 4 items an assassin could be carrying 
, when in previous seasons they really only had and the old 
(which was weaker at nuking squishies because some of it's power budget was focused into anti-tank stats and health)
No one should be able to have like 50 lethality.
