Flat armor penetration is ridiculously underpriced

Flat armor penetration is valued 40g per point, and flat magic penetration is valued 37g per point, so they seem comparable.

However, actual value of flat armor penetration is way, way higher than flat magic penetration. The reason for it is it is best against squishy targets, who have much better access to MR than to armor, and value of flat penetration increases the more the lower champions resistance is (up to cap when they are equal, ofc).

Early in the game, most squishy champions will simply have less armor - all of them start with 30 MR, while armor can get as low as 17 points. Furthermore, armor seals grant less armor than MR glyphs, to the point where many squisher champions will opt for HP seals instead. Early in the game armor penetration beats magic penetration, hands down.

Later in the game this effect would seem to be overpowered by natural armor growth, that is higher than MR growth even on squishy champions with scaling MR(melee), but it usually isn't.

The reason is that squishy champions have great MR options: , on top of usually being affected by aura. And even straight tank items like are more accessible to them.

Empirical evidences for this fact are clearly visible - is abused by every champion that has words "attack damage" in description of their kit, and , while deemed 'not a problem' by EU and NA, is already 'ridiculous and crushing soloQ' in Korea, to quote Phylol.