Armor in 2k17 lul
Why even build armor? On any champ, base armor at level 18 is ~80, and a full lethality build is ~80 armor pen. (base armor ranges from 65.5 (Gnar) to 104.5 (Rammus) at level 18) So, R.I.P. base armor. Bonus armor? Well, let's say you buy 200 bonus armor (2 thornmail armor). You still end up with less than 80 armor in total (45% bonus armor pen, 7% armor pen, 25% armor pen...), which is less than your base armor anyway. Not mentioning the % dmg increase, which are getting nerfed with tonight patch =)
You want to play macro/strategy, and punish a team for going full AD, by going tank team with armor? Armor in 2k17 lul