I think he means that certain builds....*cough* 5 Black Cleavers *cough* make armor basically useless, and the addition of percent health damage items making hp less useful (liandry's, my god liandry's on some champions is OP/blade of the ruined king), and yes to top it off the loss of resists.
So yes, in short tanks are a rather large amount less tanky, even with intended design. (I think the non unique armor pen on black cleaver to be a bug....or so I hope.)
(I am not saying its the end of the world, but yes there is a major decline in the tanky-ness of champions in the game right now.)
PS, Go play Singed With Liandry's and a Rylai's, and just watch people melt in your poison trail, its pretty dang ridiculous, if not broken.)