Here is a suggestion about crit

How about armor decreases crit damage by a small percentage. Something like 0.075% crit damage reduction per 1 armor, so at 300 armor you would take 22.5% less damage from critical hits. I mean, the better your armor is, the less vulnerable spots there would be. This would face ADCs with the choice between crit for blowing up squishies and armor pen to deal with tanks rather than just build crit to blow up everything. Also warlord's bloodlust mastery needs to lose the heal on crit portion, +attack speed is enough.