Crit marksmen

I do not understand riot current thoughts on crit marksmen, at first some crazy and probably overtuned buffs were in storage (amor pen on IE, crit reduction out on randuin) that justified the global armor pen reduction. Time passes and these buffs are taken out and nerfs for crit marksmen come trough, (randuin crit reduction doubled, bortk which is a core item to shut Down tanks will likely get nerfed the armor pen reduction stays) As I recently read that crit was ment to be the way to kill tanks but I am positive it will only be worse with mid season patch I'd like to have someone ( preferable from riot) clarifying me this issue.