LCS Masteries Questions

Looking at LCS mastery choices for our stars playing Kog, they all seem to pick Battering Blows for armor pen. This perplexes me because Kog tends to do about 50/50 armor/magic damge. Wouldn't it be much better to have the Precision mastery for mixed penetration? Is it just because Thunderlords is a weak keystone for him compared to Bloodlust/Fervor/Deathfire Touch? Even so, his 'finishing damage' tends to be magic damage, not physical damage (his r or e or q as opposed to a regular aa), so wouldn't it be better to have Piercing Thoughts for magic pen as opposed to armor pen? Bloodlust seems kind of weak since it's a small heal not often, Fervor only increases ad (but I guess it is significant), and DFT seems weak compared to Thunderlords. So, is Fervor that much better than Thunderlords to warrant not using split pen, and why armor pen instead of magic pen are my two main questions... I've also noticed that LCS players seem to like Resolve on their adcs... It seems like Cunning would be a better choice. Why specialize in dealing damage then waste masteries on fortifying a champion that's intentionally squishy? I mean, their goal is to deal damage, not take it, right?