Lethality is a armour penetration nerf? Or am I missing something.
Lets take for example 
20 Armor penetration would give guaranteed 20 armor penetration (easy right?) 20 Lethality gives guaranteed 8 armor penetration + 0,33-12 armor penetration (which depends on enemy target lvl), which means you get guaranteed 20 armor penetration only when enemy opponent is 18 level
I don't know why people are so hyped for this lethality right know, since it is huge nerf. It is for sure removing early game impact however it doesn't scale that good in lategame which was supposed goal. It would be different story if items like
would have 25/30 lethality.