If we weren't to consider the traditional runes for AD...
...at what point would 35 AD in runes(marks+quints/lvl) become better than flat 19 Armor penetration? (marks+quints)
4 Comments
At early levels, the AD is always more useful, whereas the armor pen gets stronger mid-late game, especially if you have higher base than scaling on abilities.
So the AD is better at first, and eventually the ArPen becomes better. When ArPen becomes greater than AD depends on the champion, I'm afraid I'm not knowledgeable enough on the matter to know an average estimate.
Are you talking purely about auto attack damage? There is a league wiki where all of the formulas you need to calculate this are listed. Make an excel sheet for increasing amounts of armor, copy paste till one number is lower than the other. People have probably calculated such things in the past for other values of armor pen vs ad.
Here's a video https://www.youtube.com/watch?v=WUGzzXVDiMM, didn't watch but it looks like it might at least cover some of what you're asking