Can we have the real armor formula?
You build 5-6 MR items, and you actually take much less damage.
You build 5-6 armor items, and you take 10% less damage (if that), even if they're not building armor pen.
So, obviously you changed the armor formula, and it isn't accurate anymore, nor is the tooltip in game. That, or ADCs and melee clickers are actually autoing for well over 2-3k per auto.
Imagine if armor actually did something though; Tanks would be viable and a real threat, and LC$ games would become even more boring, so you'd have to add more armor pen items that ADCs could easily build, and add more passive armor shred to champs that don't need it. (or the game could actually be somewhat fun for non-AD champs)