Armor and MR penetration are not really transparent in showing their power

Most people on GD know how it works but the average player likely doesn't understand how armor pen works or is applied. That flat is after % etc.

They don't see that their 200 armor is effectively only being 100 armor or their 45 armor is effectively only being 10 armor. They just see that they have 200 armor and it says reduces incoming physical damage by 66.7% but the LW and ghostblade the enemy has is making it closer to 100 armor for 50% reduced physical damage taken and an effective 100% health increase instead of a 200% effective health increase and 66.7% reduced physical damage taken from 200 armor.

It also has no counter, no waiting it out

Armor/MR reduction/shred on the other hand is transparent. You see it affecting you and you know that your armor got reduced by say 15% from kayle's passive or MR was reduced by 20 from abyssal scepter.

So why is this unseen power in the game? Why is it allowed to be 39% (mastery + LW/VS) or greater of a target's armor or MR?