So Why Even Use AD Runes Anymore?

I did the math on Lethality Runes and the Precision Mastery and maxing both gives you 30 lethality starting.

Do you know how much armor penetration that is?

That's 12+1 armor penetration per enemy level.

I get that AD can help with CS, but as long as you know how to last hit without them then why even use them?

I personally think Lethality Reds are over tuned. 3 of them together are 50% stronger than ONE Lethality Quint.

I could be wrong, but shouldn't Lethality Reds have been nerfed along with the items?