His E is decent CC, I'll grant that. But Darius is more of a carry than a tank. Tanks (in my mind) are another form of support. They aren't suppose to carry, they are meant to help their carries carry. It's probably why we see a lot of tanks support (
) even when they aren't secondary support.
Obviously this causes issues between tank supports and non-tank supports (which season 5 had a lot of complaints with). Tank supports provided a lot of lock down, which was great for ADC's because a target that can't move is easier to hit (I could make an insult to ADC's, but their job sucks in my opinion so I won't). Non-tank supports however had to provide other forms of utility (like healing or displacement rather than just lock down) and are as or more squishy than their ADC.
Having at least one tank on the team is very important (otherwise
goes unchecked since it is not common for non-tanks to have reliable (non-ultimate) CC) so if they don't go in top or jg, then they'll be put in support. Since a midlaner can offer some utility (I'm generalizing) like a utility support, not much is really lost.
Honestly the best example of a tank I can think of is
. He has hard CC, a taunt, and really hard to kill.
But
are not tanks. They are Fighter/Tanks. They might be called tanks because the fighter class is incredibly broad (kinda like how supports are broad) and very generalized since we have champions like
who classify as fighters. The difference with these two is that they aren't really "tanky" (
will be built tanky because he's basically a stun bot if he can't end the game fast enough) but can be built tanky so they can last in a fight.
Course you can build anyone tanky, but what matters is how well they benefit from it. You don't really build assassins like
or
tanky as it doesn't benefit them over damage.
on the otherhand benefits extremely well from tanky items because his entire character is built around not dying. He isn't a tank though because he doesn't provide much in teamfights as compared to
or
. He's just a tanky motherfucker who gets people to focus him by simply existing (because no one is able to just ignore Mundo in soloQ apparently).
TLDR: Tanky =/= Tank.
Note: I could be wrong on some champion classifications. I don't know if
is secondary support.
is a fighter/tank that has been shifted into support by the community though, so supports aren't the only class that can support.