Melee champions vs tanks, someone explain to me.

Imma use this example cause it just happened. I'm playing Yasuo vs Voli. In our first real fight my build looks something like(i dont remember exacts) Pd, tabis, vampiric, Ec. Voli's build had righteous glory(an item in need of gutting because why does it offer so fuckign much, but that's not the point of this post) and boots, he might have had a some armor item, but not much. In every scenario, I should have the advantage, 12% damage reduction from pd, 10 from tabis, lifesteal, slowing any healing he is doing, bone plating, pta, everything to advantage me in a fight. Voli torn me a new fuckign one each trade. Not that he outplayed me, I only lived half the time cause trades where always in my favor in that I was controlling the fight, but could not muster half the damage he is doing.

Someone explain to me why this isn't broken to all fucking hell. Yeah he has a little more hp and armor, but my damage reduction and lifesteal should still throw the fight to me, but not fucking once.