Actually, yes, armor is useless unless you're stacking it to Malphite/Rammus levels of derp or have a massive personal armor steroid like Leona. Short of that amount, Black Cleaver and proper spam of Armor Penetration will reduce your armor to zero or next to it. If one Black Cleaver doesn't give them true damage, then they just buy a second one.
Riot has effectively killed tanks which are not Mundo and Sejuani, who can get away with stacking derpass amounts of health because it actually gets them something and That Which Must Not Be Spoken Of has yet to be imported over from TT, probably because Nome actually read at least 30 seconds of the outrage caused when he brought over BFT.
Of course, I just mentioned Sejuani and implied a degree of usefulness in one sentence, so that was all just invalidated.