See that just isn't true.
Individually yes he doesn't really stand a chance vs tanks.
But tanks are front liners, they basically have no choice but to take Black Cage to the face, while the same Black Cage zones his entire team allowing for enemy team ADC to ram its peen up your Tanks rear end.
Assassins? just Q+W+E+R directly on your own face, and they get assassinated before you do. Atleast post midgame that's the case, not so much early game.
Get caught off guard? Zhonyas first, and then QWER on your own face.
To many targets able to reach you?
Eh who cares, build pure tank, still have 600AP and 1shot 4/5 of your enemies. while have 150 armor, 150MR and 3500 health.